Saw one of these in the store today and convinced myself very quickly that it would be useful. And it is. 
 
My problem is playing guitar in the evening - I have to play through headphones and it's a bit of a drag to have to load a guitar sim and set the inputs up yada yada...plus being tied to my computer. I always end up just playing my Tele unamplified, and I never did like playing electrics "acoustically" so to speak. 
 
Now I have the AC30 amPlug plugged into the guitar so all I gotta do is plug the headphones in and we're off. This thing really does have a great sound for what it is! My Tele sounds GREAT through it. You get a bit of crunch if you crank the gain up, but not too much, and the clean tone is beautiful. There's a bit of hiss when you have the tone control turned up, but it disappears when you set it at about 6 or less, and besides which the sounds starts to get a bit too brittle above that anyway. I find it helps to turn the tone knob down quite a bit on my Tele as well. 
 
Overall this is the best $40 I spent in ages. I'm walking around my apartment with the guitar strapped on. I haven't tried the other models (or the Vox headphones) but I suspect they're all pretty good. Build quality is a bit light, and you gotta be careful where you put your guitar down when it's attached, but I'm not worried about that. Great buy. 
 

I've got one of those and I kind of forgot about it. Some one got it for me at Christmas one year. I'll have to dig it out again and give it another go.

You forgot to take the sticker off your Tele.

Never!

Is it better than a Scholz Rockman or a Lil Smokey (Marlboro)? I had forgotten about them.
So how does it sound? I mean.. do you like the way it sounds?

Have never tried the units you mentioned. I like the sound, obviously it's not quite as good as the real thing but for just blowing away on your own late at night (perhaps I should rephrase that) it's great. You have to play with it to get a good sound, obviously. And I can't speak for other guitar models but my Tele sounds great through it. I guess if I could have one improvement it would be a little reverb, but I'm not too bothered about that. I hear the lead version has reverb? Might be worth checking out the Vox guitar headphones as well because I think they have effects on them.

One obvious point is that it helps to have a pair of good quality cans - you're not going to get a great tone listening on your iPhone buds.

Oh and forgot to mention there's also an aux out so you can plug into your interface and record.

Oh and forgot to mention there's also an aux out so you can plug into your interface and record.

I used to have a Rockman (until the batteries burst and killed the thing).  That was WAY more than just a headphone amp (plus it clipped to your belt like the Walkman it was named after).  It had distortion and other cool effects.

Is there an AUX so you can record??