I tested this extensively with an Ibanez RG42 with the Infinity Humbuckers, and a Fender USA Strat with a Seymour Duncan Strat-sized Lil '59 Humbucker. I used a Planet Waves 12' guitar cable into the amp, then a normal amp speaker cable to a 1x12 closed back cab loaded with a Celestion Vintage 30 8 ohm speaker. So the signal path was quality from beginning to end. At first I was really digging this amp, as it has the all tube response and feel that I expected. In fact it was a better feel and response than I expected as I'm used to Class A/B, which are a little saggy feeling (as opposed to snappy feeling like this Class A). That's the best I can describe it, as the amp seemed to have a lightning fast response, which was good. The clean sounds were great, very harmonicallly complex as you'd expect, and the distortion (everything past 12 o'clock) got progressively more rich. If you want to know what the distortion sounds like, play Steely Dan's "Reelin in the Years". That's it. From about 3 o'clock upwards things start to level out soundwise, and it may get slightly louder, but it doesn't get much better. Both guitars sounded different and I feel their true nature was reflected in the output. HOWEVER... at anything past 10 o'clock, this amp has an upper high frequency noise which sounded like what you hear when your ears are ringing. A piercing sound that was like an icepick in the ears. I first tried dialing this out with the tone controls on the guitars to no avail. I then stuck an eq in front of this thing, and again no luck. I then played this exact set-up through my Fender Hot Rod Deluxe (same guitars, cables and speaker cab) to check, as I thought maybe my ears ARE ringing. Nope. I tried the eq's on distortion pedals, and then I rigged an rack mounted eq into the signal chain before this thing, and still, that f'n sound. Very, very sad as this amp actually sounded and felt good. I thought maybe it's the tubes, but I doubt it as I know what microphonic tubes sound like, as well as about-to-blow-reduced-output tubes, and this wasn't it. Have someone scream into your ear for a few minutes, and then go into a quiet room and listen to the ringing noise, amplify that sound and that's it. Maybe it was just this particular amp, but I quickly sent it back. I had a suspicion that $99 would buy a flawed design made of the cheapest components that it's possible to source from slave labor. The sad part is that for many people, this will be theirs, or worse yet, their kids first tube amp, and they'll get past the return date before they notice this, by which time they'll actually have tinnitus from the sound, so they'll be double screwed. I wasn't too happy about this, and yet it could be a one-off situation so I'm not going to give this category a rating.
This thing felt really well built. Quite heavy, and packaged well. However, when you strip out the sellers profit ($20), the shipping cost from China ($10), Epiphones profit ($20), the cost of the packaging ($3), the Chinese manufacturers profit ($20), Labor ($10) you arrive at approx. $83 cost, leaving approx $16 worth of parts that actually compose this thing. So no, I would not gig without a backup. Since all amps have this cost structure to some degree or other, I would not balk at paying $600 to $700 for a decent amp. At least then you'll be gigging with with about $100 bucks worth of parts, including some additional tone controls.
I've tried several low cost solutions over the years that seemed to-good-to-be-true (digital modeling anyone??). $99 for a quality tube amp is not possible and I would advise you to buy something better. There is a reason that Gibson gets $500 for this same amp configuration. People think it's the name, and they're right. Gibson gets $500 for this same amp because the Gibson name means very high quality design, parts and build. For kicks, I went to a music store and played the little Gibson 5 watter, and yep, it's how this one should sound. Damn, it's $400 bucks more, which I can't afford right now, but at least I learned something.