My Allnic phono stage uses this rectifier and I’ve rolled a bunch, including the GEC U52 (both brown and black base) and the Mullard metal base (really a Philips-Miniwatt, Holland), as well as various bakelite Mullards and a bunch of others.
There’s a great resource if you look up Dubstep Girl’s Massive 5AR4 Rectifier Shoot-Out. She compares a huge number of different rectifiers (some equipment may not allow for the use of a non-direct "equivalent"). To me, it’s almost like a tone control and the choice I make may not be yours, depending not only on subjective preference, but circuit and system.
Old stock rectifiers used to be cheap, not anymore.