I have one, its a 24kw one with a 65kg hopper. needs cleaning out about once a week, filling every other day when used during wintertime. needs almost no cleaning or filling during summer when it runs the DHW only.
Pro's - great for people like me who dont have gas and my location means that even oil is a pain to get (I live the other side of a river with no vehicular access for 70m to the house).
pros:
quick payback on the system cost, around 3-4 years for me
RHI easily covers the cost of the pellets and servicing
'green'
cons:
gotta buy and store pellets
regular filling and cleaning
your control system will be different, you cant use a switched demand type of system so that the boiler responds in the traditional way, you could either make a buffer the demand which acts as a, well, a buffer
or leave your zones to work as normal but without swiching the boiler on.off, but run the boiler on timer/manual and demand is fulfilled then.
I use radiators with mine, 2 zones plus a DHW zone, I reckon it would be amazing with UFH.
I have 2 boilers pretty much the same, one of them runs my barn/workshop and that will be registered soon with the commercial RHI.
I have lived with them for a few years now so and specific questions, ill do my best to answer as im sure I will have missed some points.