I have one of the older versions of the US 50 with the dark brown exteriors. I really can't recall when I purchased this amp, but I remember needing some sound reinforcement for when I led worship. At the time, the Ultrasound Amp was "the" one to get - and rightfully so. Great sound, great price, and great feature set. I've always found it to be a perfect companion for my K&K equipped acoustics and found it easy to dial in the sound I wanted. The effects are pretty decent, but honestly, I only use a bit of reverb for the most part. I have found the tone to be quite natural, a good reproduction of my guitar.
I have an older version of the is (DS2) that I've owned since 2004. I must say that this is an absolutely fantastic amp. Crystal clear tone with no coloring of the sound. Very good digital effects of which I typically only use small amounts of reverb. Never overdrives, never distorts, unbelievably reliable. Between this and the DI Plus Direct box I bought at the same time, I simply have what I believe to be the best acoustic setup possible for just about any venue for this price point. Mostly leading Sunday Church worship, I never have problems getting exactly the tone and volume I need through the PA. Playing out in coffee shops and at numerous weddings, I never worry about being heard or overpowering the places I play. The tone of my Taylor Guitars (414ce LTD, 514ce) is clean, clear, and completely natural. My 414ce has the Expression system and my 514ce uses a Baggs Element Onboard and I have yet to find any better combination than what I have right now and am very reluctant to try anything else.
I purchased this amp a number of years ago from Shoreline and it has not disappointed me. For the price, it is an excellent acoustic amp, that doesn't "color" the sound, just makes your acoustic guitar louder. I've used this amp plenty of times at weddings, etc., and to serve as a stage monitor. It is a great "workhorse", providing you're not playing at a large venue.
I also use this amp with a Baggs Para Acoustic D.I. box for some added "oomph" to the volume. A great value.