I own one mares syncro tech.
Before i got myself a BP / wing that was what i used. I've done about 130 dives with it and would not recommend it to anybody. As i brought it I was not a very experienced diver, and in my eyes the thing looked robust. But it really isn't. Underneath the soft backpack, some italian desinger has hidden a lot of velcro straps and strange buckles, making the thing awfully complicated to manage and adjust. And with doubles some of that low-tech velcro-stuff has a tendency to give in, making things even more complicated. I've ended up quite a few dives with dislocated doubles, as the backpack has partly detached from the harness of the mares.
Also, there are way too many D-rings on it. Mine had 10 S-Drings orignially. I soon cut off all but a few... And many exhausts as well... except for the inflator which has two exhasts, there are THREE additional possible faliur.... exhausts.
Additional clutter includes two 'unreachable' velcro pockets on either side, an integrated weight system and a front pocket. The front pocket is actually pretty handy, but unfortunately very much in the way.
The integrated weight pockets are a bit too small for most lead-weights... removing weights underwater is managable, but putting them back in certainly is not.
well, i could go on talking about the thing for ages, since it has caused my lots of headache, and boring DIY repair, but i leave that to someone else...
However, this was only my opinion. Maybe other people find it nice...
Regards
/Kristian