I should begin by dispelling a myth or two: it takes more than a Wurly to sound like Supertramp! A plain Wurly sounds quite a bit different; they used a ton of effects and amps to get "that" sound. Mr. Tramp sounds like a plain Wurly, not like "Goodbye Stranger." But trust me, this is a Good Thing! You can still get that glorious, if processed, sound; I recommend beginning with the Simulanalog and Classic suites for some real vintage quality. Amplitube and Trash also rock serious ass.
Anyway, Mr. Tramp sounds and responds like the real thing. I didn't believe it either when I first played with the public beta, but a trip down to my local Banjo Depot (Err, Guitar Center), which had a well-used but well-maintained Wurly (a 203e, IIRC) that matched this emulation. It's a mellow, thin, hollow, reedy kind of sound that really responds to sensitive treatment. It's a friendly, good-natured sound that just works -- but you can dirty it up and sharpen the edges, give it some amphetamine-fueled aggro with the right amp sims.
I've never had any problems with it whatsoever. It says what it does and does what it says, with no surprises (other than how good it is!). I wish it had a more flexible tremolo, but it exactly matches the real thing. Anyway, Guido is almost unreasonably responsive to suggestions and genuinely cares about his creations -- and it shows.
If you have any interest in a vintage sound, do yourself a favor and download this.