The first time I used this system, I gave the lapel mic to the pastor and let him use it for a sermon. I had to play with the EQ on the mixing board to get a natural sound out of the mic, but that wasn't a big deal. Something interesting did catch my ear, though. Whenever he was talking, there was a background hiss. Not loud static or ear-blasting fuzz, but a small background hiss. After a while, the hiss went away, or maybe I just got used to hearing it.
Anyway, I played around with it some more with my guitar and the hiss was back, only far more pronounced. Whenever I hit a note, there would be a definite backround noise. Figured that maybe it was my pedals or the amp, but there wasn't any hiss when I played with a cable. Plugged the wireless back in and the hiss was back. It was more noticeable on quiet, single notes than it was on chords, but you could always tell it was there. I EQ'd out some of the higher bands with my Boss EQ-20 and that helped quite a bit, although it didn't completely kill the noise. Btw, I play with an NS-2 in my pedal chain too, and that didn't take care of the noise either. I've noticed that the hiss isn't noticeable at all when you're playing with a band. Pretty pronounced when you're playing alone, though.
Other than the noise, I like the sound quality of the system. It doesnt' color my sound too much--maybe a little bit more high-end than with a cable--but it sounds good. I guess my only other complaint is that I lose some volume playing with this. I can't keep my guitar at normal volume 'cause I'll constantly peak on the receiver, but when I turn my guitar down so that it doesn't peak the receiver as much, I lose quite a bit of volume. Even with the volume on the receiver turned all the way up, I'm pretty quiet. I make up the volume difference with a Boss CS-3, so it's not a huge deal, but it's still something I think AKG could've done better.
Just a note: I'd probably rate this with an eight or a nine in this category if it wasn't for the hiss. That really takes away from this system, IMO.
When I purchased this, I anticipated a piece of Austrian-made gear. All the other AKG items I own were made in Austria, although this one was not. Made in China, just like everything else these days. Oh well...
That aside, the receiver and transmitter both seem solid. All metal case on the receiver and all the knobs and switches are solid and don't feel cheap at all. Pretty much the same for the transmitter. I've got it all mounted on my pedalboard with Velcro and I don't anticipate it failing or breaking any time soon.
As for whether or not I'd gig this without a backup, I don't think I would gig any wireless system, regardless of the manufacturer or quality, without a cable for emergencies. I've always got a supply of guitar cables nearby, just in case something acts up.
Outside of the hiss, the volume loss, and the fact that it's not made in Austria, I like this product. The range is decent, although I haven't gone more than 50 feet from the receiver yet. I haven't experienced any interference, and I've got three other channels to choose from if I ever do.
It's really a great feeling to be free from cables. I can walk back to the mixing board to change a setting and keep on playing, I can walk around stage without having to worry about tripping over my cable--it's a great product in that sense.
If this was stolen, I'd probably buy another wireless system, although I don't know if it'd be this one. It seems to be one of the more highly-regarded systems in the price range, although I might look into a Shure or an Audio-Technica if I had to buy another wireless system. Overall, it's a good product--it certainly has a few caveats, but it gets the job done.