Beryllium-Copper: How safe?

The problem with Be in speaker driver diaphragms is that it is so brittle that it atomizes, making it float in the air and easy to breathe, so your chances of getting a health risking dose when they break is non zero, but even then the risk of toxicity is low.

Keep in mind that beryllium copper connectors are generally plated with either gold, silver or rhodium (sometimes very heavily plated - as in the case with Furutech).  So, even though beryllium alloy may have a slight risk of being toxic, you would really never get to that "beryllium" metal through the plating, unless you used a grinder or scraper against that metal (which is highly unlikely unless you just wanted to ruin your connector).

As long as we're on this subject, how about Beryllium tweets?

Though it is commonly believed that Copper Beryllium alloys are safe to handle, evidence suggests this is not true.  There are many factors that make copper beryllium dangerous such as corrosion, microscopic amounts of dust on the copper beryllium that can enter through open pores or cuts and product specific problems, such as shaving from a copper beryllium tool slipping and causing exposure to beryllium particles that can be breathed in.  OSHA has recently reduced exposure limits to beryllium to 0.2ug/m3.  

Here is a study in the Chest Journal outlining a case study of two women who developed Chronic Beryllium Disease from just handling Copper Beryllium products. https://journal.chestnet.org/article/S0012-3692(15)38252-0/fulltext#cesec10

Apple, the tech giant, has removed all Beryllium including Copper Beryllium.  https://www.apple.com/environment/safer-materials/

The information about beryllium dust vs the beryllium/copper alloy is correct.

Take a ride with me in my way-back machine. Decades ago when I worked in environmental control one of the sites I inspected was a beryllium smelter. I think it was the only one in the United States. Since I was told the ore came from South America, I always thought it was funny that the plant was located in my territory in a small town in northwestern Ohio.

The smelting and machining processes required strict environmental controls and personal protection including respirators and skin protection. The finished beryllium/copper alloy products (non-sparking hand tools)were safe to use without gloves. In fact I saw their non-sparking drum wrenches in use at many of the other sites I inspected.

Bottom line, don't worry about the alloy.

Geez, I have a set of beryllium copper golf irons that I don't use, maybe I should visit e-bay.

As stated in Albert's reference, it is my understanding that some years ago, stricter environmental controls increased costs related to manufacturing items with this material.

When beryllium is alloyed with copper it's safe (unless you machine it or something like that). The dust then can be dangerous. A solid chunk of pure beryllium is harmless. A good analogy is mercury fillings. Mercury metal is toxic, but when alloyed (amalgamized) with other metals, it's safe.

From Wikipedia

As beryllium is toxic there are some safety concerns for handling its alloys. In solid form and as finished parts, beryllium copper presents no particular health hazard. However, breathing its dust, as formed when machining or welding may cause serious lung damage. [1]Beryllium compounds are known human carcinogens when inhaled. [2] As a result, beryllium copper is sometimes replaced by safer copper alloys such as Cu-Ni-Sn bronze.[3]
[edit]Uses

Beryllium copper is used in springs and other parts that must retain their shapes during periods in which they are subjected to repeated strain. Due to its electrical conductivity, it is used in low-current contacts for batteries and electrical connectors. Because Beryllium copper is non-sparking but physically tough and nonmagnetic, it is used to make tools that can be used in extremely cold environments like Antarctica. Various tool types are available eg screwdrivers, pliers, spanners, cold chisels and hammers [4]. Another metal sometimes used for non-sparking tools is aluminium bronze. Compared to tools made of steel, Beryllium copper tools are more expensive, not as strong and wear out more quickly. However, the advantages of using Beryllium copper in hazardous environments outweigh these disadvantages.

Example of a non-sparking tool
Beryllium copper is also frequently used in the manufacture of professional-quality percussion instruments, especially tambourine and triangle, where it is prized for its clear tone and strong resonance. Unlike most other materials, an instrument composed of beryllium copper will maintain a consistent tone and timbre for as long as the material resonates. The "feel" of such instruments is rich and melodious to the point that they seem out of place when used in darker, more rhythmic pieces of classical music.
Beryllium copper has also found use in ultra-low temperature cryogenic equipment, such as dilution refrigerators, because of its combination of mechanical strength and relatively high thermal conductivity in this temperature range.
Beryllium copper has also been used for armour piercing bullets, [5] though any such usage is unusual because bullets made from steel alloys are much less expensive, but have similar properties.
Beryllium copper is also used for measurement-while-drilling tools in the directional (slant drilling) drilling industry. A few companies manufacturing these tools are GE (QDT tensor positive pulse tool) and Sondex (Geolink negative pulse tool). A non-magnetic alloy is required as magnetometers are used for calculations received from the tool.
For a time, beryllium copper was also used in the manufacture of golf clubs, with emphasis on wedges and putters. Many golfers prefer the soft feel of BeCu club heads, particularly for chip shots and putts around and on the green, where an extra measure of control is desired. Due to regulatory issues and high costs, BeCu clubs are hard to find in current production. Vintage and pre-owned examples remain in demand at used club shops and on Internet auction sites.