I used this box with a variety of different instruments: An 89 Ibanez Jem, a 94 Ibanez 442R, a Yamaha APX6 acoustic guitar, a Roland GR-1, and a Korg X-3. The unit was very useful in a varity of ways for each and every instrument, and also had patches for live drums and vocals that I was never able to put to use. Very flexible. The unit has a built in noise gate for every program, and thus noise was never a factor. I tended not to use the built-in distortions since I record direct typically, and few of the distortion chains have a speaker sim. I ran from a Whammy to a Zoom 9002 (for some distortion, a tad o' compression and eq) into the A2. Occasionally I went from to an IPS33B harmonizer before hitting the A2. The effects were quite strong. The reverbs are of near-Lexicon quality, and can get really huge. Chorus effects were quite variable, from slight to dense. No pitch shifter per se, but it did have a good detuner. The fact that it handled stereo in and out was a big plus for keyboards and guitars.
When I ran through an amp, it was a 100 watt 2x12 Crate amp, which I prefer for the lack of sonic coloring they do. It sounded very good through the amp, although my beat up amp did cause some interference noises if I set it right on top of the cabinet.
I typically do instrumental rock and fusion (Steve Vai, Joe Satriani, Chick Corea, Frank Gambale) as well as some techno stuff, and was really happy with how well I could emulate certain sounds. In fact, once I became more comfortable with the unit's controls, I could really make some incredibly thick but clean guitar sounds whether I was clean or dirty.
I was particularly impressed by the reverbs and compression. Outstanding for the price.
The unit seems to be pretty stable. I carried it around extensively without a rack-mount and never had any problems. I'd definitely feel comfortable using it without a backup unit.
I would consider the A2 an incredibly good deal and match for any kind of music. After 7 years of playing I've used stomp boxes, processors, and straight into amp/board setups. This was definitely the best sound for $400 I've heard. It'd still be great at twice the price. With better distortions and harmonizing it'd be a great stand alone/plug & play unit. If the device were stolen, I'd probably try to replace it with the same unit or it's big brother the A1. The sound quality really blew me away. I was quite fond of the quality of the output signal. Very few boxes can be recorded with the first few hours you own them. This sounded killer whether it was used as a main processor for guitar/keyboard, or used as a general mix-down aid.
If you can find one of these for between $400 - $600, buy it! It's a great addition to the project studio, since it's not just a guitar box. For guitarists, it's the missing link between very glitchy reverbs & chorus and faking a Lexicon. Easy great sound without dropping four digit figures into a single piece of equipment.