Impartial advice is difficult to come by!
I love my SBS, it's comfortable for me, comfortable for Saff and hasn't caused a days problem. She's got a good back with no atrophy and she's been in the SBS for 3.5 years now. I'm definitely going to buy a Vogue when I get the money.
That's just my opinion though from my experience and from seeing other horses ridden in the SBS and Fhoenix who have never had a problem. There are people out there who will tell you (and have told me!) that these saddles are wrecking horse's backs. Often these people have a vested interest, sometimes it's just a case that the saddle that they tried didn't suit their horse, sometimes there's a story behind the story that you've not been told and it's actually not the saddle's fault at all but something that was done, unwisely, by the owner!
Like anything not all treeless (or part treed or soft treed) will suit every horse or even every rider. It's a case of seeing if you can try different ones and see what you think.
In both treed and treeless saddles pressure testing has showed that what can make a big difference to the saddle is the way that the rider sits. More pressure was seen when a rider sits in a chair seat for example and a driving seat is a big no-no.
The best thing to do is to have a look at as many sites as you can, ask for opinions, have a look at the saddles yourself, try some out and then make an educated decision from all of that
One point that I would make is that treeless saddles DO feel different to treed saddles and more so when the stirrup bars are set back. You have to ride in it more than once to get a true feel for whether or not you'll like it because it does feel so different. I, for example, nearly ended up on my nose when I first got my SBS because I was used to having to pull my legs back in an effort to achieve the 'ear/shoulder/hip/heel' line. Doing that in the SBS (with the set back stirrups bars) meant that I was tipping myself forwards.
Which area are you in?