What is the forums opinion of SVS subs?

I own one of each, a REL S2 and SVS SB1000 Pro, and I prefer the SVS. They augment a pair of OB speakers in a 16' x 21' room to great effect where you feel immersed in the sound.

As @soix mentioned, 2 subs better than 1.  Easier to get good sound.  3 subs even better!  Multi-subs are able to smooth the lumpy bass found in all rooms.

A while back I managed to borrow 2 ported subs to play with and found them a little difficult to place and that is why I chose the SVS sealed unit. I placed the SVS in the rear right corner and the REL about middle of left wall. Omnimic confirmed a better room response than the 2 ported designs and that was before any fussing over their positions.

The SVS has continuously variable phase adjustment and with the ability to change settings from the listening seat is a great help. In addition to phase there is also low pass, parametric EQ, room gain compensation and presets.

The REL ( it's the S2 I think) which I found used at a bargain price was placed along the side wall so I would have the option of moving it about for best integration because the phase is only switchable from 0 to 180 degrees.

Setting up these 2 was a breeze. With Omnimic guiding me I moved the REL backwards and forwards, each time readjusting the SVS then move REL again and further tweak the SVS and so on. Will now build myself a servo-sub to add to the fun.

@ratboysr, I may be wrong but I get the impression you think it necessary to have all subs in a multi-sub set up exactly same model. You are free to use a different type and in fact may prove beneficial. For example when helping a friend with 3 subs, 2 of them 10" and 3rd 12" my measurement showed a stubborn partial null at about 70Hz. Floor space was a bit lacking so I brought over a 6.5" little sub in a 9" sealed cube. After some experimentation found it worked wonders placed about 4ft off the floor on a large bookshelf.  Measurement confirmed the the null had improved from -10dB to -4db.  The small sub was about 5ft away at almost ear height so would not need much power but received enough to further smooth out the room response. In fact when turning up the volume on this sub I could fill in that 70Hz completely but raised a nearby peak a couple of dB. I erred on the side of caution to protect the 6.5' driver.

Generally it is best, for easier integration, to stay with sealed boxes. Multi - subs are transformative and I am constantly surprised by the reluctance to accept/ embrace the concept.