The TASCAM US 20x20 is a nice-sounding, full-featured pro unit (Word clock, various Digital in/out, good softmixer, etc.). Great quality and bold features for a great price.
As to the latency, the latest drivers improved things somewhat - I'm down to 9 ms roundtrip on USB 2 (older, win 7 computer - I'll check with my newer one running USB 3 when I get a chance). By no means top-of-the-class but usable. Over a 1/3 of that is getting sound in and processing - the output latency solo is 5ms or so. That is what you'll get w/ softsynths to work with.
And, for what it is worth, TASCAM has in-house driver writing now and the US line (2X2 on up) use the same drivers so I expect new ones to continue to come out. Of course, I've been wrong before and I would never buy hardware if I could only use it in the future with more work (been there and done that) but I find the latency is OK for my work.