Single channel valve head with bass/mid/treble tone controls, preamp (distortion) control, master volume, boost switch (added overdrive and tonal change), low power switch (brings output down to 0.1 watts), 8 ohms and 16 ohms speaker outs, power switch, single guitar input.
Real Marshall tone and response, low volume, EXTRA low volume low power mode, small, light, solid build, price.
No presence control.
Haven't had it long enough to judge.
The JCM1 aims to reproduce the tones of a full-size JCM800, but at usable volume. And it DELIVERS! The characteristic JCM grind, crunch, chunk and aggression are all there. The amp is responsive to dynamic playing, reacting very much like its big brother - palm-muting bass strings produces that classic Marshall "thump" (think 80s Gary Moore), pinched harmonics scream (think 80s Gary Moore again), riffing is grinding but articulate (think classic Accept), put an overdrive in front of it and you can get much more "metal" tones (think Zakk Wylde), roll off the volume on your guitar you get glassy, edgy, Marshall valve tones.
The boost switch on the from of the amp is supposed to change the characteristics of the amp to emulate the Silver Jubilee series Marshall. Having owned both a JCM800 and a Silver Jubilee, I can tell you it does sound more Silver Jubilee-ish, making it more compressed and springy with more preamp gain.
Something that I ought to address is the issue of volume. Judging from the reactions I've read to the 1 watt Marshalls (or other 1 watt amps for that matter), I can only conclude that very few people know how loud 1 watt is. A 1 watt amp is 31% as loud as a 50 watt amp. Don't believe me? Read this: http://www.amptone.com/g112.htm - The reality is that if there are other people in your house or if you live in an apartment, the JCM1 on full volume is still WAY too loud, even if you stick the cab in a closet or the next room. Is it loud enough to rehearse with a band? Not sure - it would depend on your cab and how loud your drummer plays.
Anyway - regarding the home use issue, Marshall have gone a step beyond the other small wattage amp makers by adding the option to cut the volume down to 0.1 watts (via a switch on the back), which Marshall say is for "personal practice". That's still 15% as loud as 50 watts, but it is usable, even in an apartment and most importantly, it STILL sounds good.
The tone controls are very much like a big JCM800 (i.e. not very effective) but you don't buy a JCM800 for versatility. Having said that, I would have preferred to have a presence control. The amp responds very well to being pushed with overdrive pedals (I have a TS9 and an OCD).
Tone-wise, this thing is bloody marvelous. With the JCM, I'm using an alder-bodied superstrat, with a Floyd and a Seymour Duncan JB. My cab is a Marshall 1x12 open-back with a Celestion vintage 30. The sound coming from the speakers is something to behold... These are the best tones I've had since I sold my Silver Jubilee Marshall head. The reason I sold that was because it was unusable at home and I wasn't (and have not since been) in a band. Enter the JCM1. Problem solved.
I ought to mention the price, as I rated that as a plus point. I've read several comments on the Internet where people have said that they feel the amp is rather expensive, especially as it's only 1 watt. How much is good tone worth to you? This amp costs less than HALF the price of a real 100 watt JCM800, which is unusably loud for home recording. The JCM1 is three times the price of a Blackstar HT1 head, but there is NO comparison - the Blackstar is a joke compared to the Marshall (I know - I have both).
A final word of warning though for anyone considering buying this amp for recording. This is obvious to many, but I'll say it anyway... Whilst this amp may be aimed at home recording, to get this type of sound recorded well, you're still going to need the engineering and production chops and gear too. The sound coming from your cab might be pure vintage Accept, but it's not going to make it onto a recording like that unless you have the skills and gear of Michael Wagener.
But the amp itself? Pure Dino. And I love it.