I must say that my enthusiasm over the recent Synchron products is, well, muted... no con sordinos which is a "must have" for me. Between that and the disappointing legato intervals in Synchron strings I am much more cautious and concerned about buying more of these products.
Top be fair you should consider
a) VSL has been always the only Producer who provided a complete Set of muted articulations as Volume II of Chamber, Solo, Appassionata and Solostrings. So you cant judge the whole propject from just the first Volume
b) what the other Competitors provide is either just the Filtertrick (which you already can do now with Synmchron-Strings I by simply closing LPF12) or even worser they provide in general just one or two sordinio articulation making it nearly impossible to work musical reasonable with sordino passages which are anything else than just smooth stringchords,
In my humble opinion (after having already produced nearly an hour of ambnitious classical music with SyStr.) there is no real evidence for any substancial lack of legato, while it of course it may be that some people who didn't worked yet that seriously with that library might be the victime of their missing expierience to get out of it what they are looking for.