I was thinking of writing a review for the forum, then saw your post, so here goes...
I bought one of these a month or so ago, along with the matching 2x12 cab, and I've now done a few gigs with it. My previous amp was a Roland JC 120. The Lionheart is my first valve amp, but moving to valves from a JC 120 isn't such a great leap as from another SS amp, as the Roland is pretty warm despite being solid state. However, the JC 120 is bloody loud, and I couldn't even have it on 1 at gigs, below which it gets a bit muffled. So I decided to look in to a smaller amp, and having always hankered after something with valves I asked advice from a guy I know.
He runs a recording studio/rehearsal room complex in which he has mostly Laneys and Marshalls. He has 40+ years of experience with amps, and is also in a band himself. He also plays a semi-acoustic, like my 335. In short - I value his opinion. He loves the Lionheart, and recommended it to me. As he had two but only used one, I bought one from him at a good price. My chain is now 335 (with BK Mules) > EH Black Finger > Mojo Hand Mule > George Dennis volume/tremolo > BOSS DD3 > Lionheart.
For me, this amp is wonderful. I don't want hi-gain, I want a nice vintage sound, warm, sparkly cleans, crispness, twang, growl and attitude when I need it. My band plays what I refer to as "indie-blues", and the Lionheart is perfect. Yesterday I just sat in front of the amp strumming a chord, and listening to the harmonics as the guitar rang on, strummed another chord and listened ... - it was lush, rich, full - and that was with the volume on 1!
Is it loud enough? Absolutely. I'm conscious of having this thing on 2 in the house because of the neighbours. (I think the closed-back cab really makes a difference.) At gigs, I can have it on around 5 or 6 and not get told off by the sound man - it's clean at that volume, but has a rich attitude about it when I pick harder: it's extremely responsive to picking weight. It also takes pedals well. Tone-wise, I have the bass on 5, mid 8, treble 7, and the tone control on 7; reverb is on 5. To my ears this gives a nice compromise between clarity and mellowness. Set the tone control at 9-10, and there's a jump in the higher frequencies.
The controls are relatively simple. I can see people feeling the tone and reverb controls don't do much, but I've found that you get more perceived reverb with the tone down below 7 than when the tone's set higher. Besides, this amp's about subtlety and taste rather than being in yer face.
I mainly use the clean channel, sometimes with the Mule to add grit, and use the drive channel when I want a loud boost. The drive channel has two controls: "drive" and "drive volume". Setting a low drive and loud drive volume will give you a Bluesbreaker type sound - a nice open, crispy output-valve distortion, but not bags of compression or sustain. More drive and a lower drive volume makes the preamp valves work harder and gives a tighter, more punchy rock sound, greater sustain. I have the drive on 7, drive volume on 3+, which sets the drive at a slightly higher volume than the clean, which is what I want.
I haven't tried it with a high drive and high drive volume, come to think of it - I might have to give that a go just to see what it's like!
To me, as someone who likes a vintage sound and wants a superb clean sound, and to be able to hear the guitar rather than the fuzz, this amp is fantastic. It's got four EL84s and three 12ax7s. Count 'em, go on. If you want a more rock sound then you might want something with more gain on tap. Not me. I now have an amp which I have had to learn to play as much as I play my guitar, and that's got to be a good thing.
Ladies like the blue tolex. Even sound men and drummers comment on my amp, and that's saying something, right?