That was my first muzzleloader: a .50 flint GPR. My initial impressions after first benching that rifle over sandbags were:
(1) I was absolutely shocked at its inherent accuracy - much better than anything I'd expected. The barrel, at least in mine, is most definitely a keeper!
(2) The Lyman flint locks themselves are pretty sad: weak (coil) spring; soft frizzen; bad cock-to-frizzen geometry; rough sear with poor geometry; etc. (L&R RPL-05-F is a MUCH better lock, especially once tuned according to instructions in the Peter Alexander book; it's not exactly a "drop-in", but pretty doggone close, with a little careful inletting.)
(Once I got the new lock tuned and installed, spark-to-ignition time still seemed a little dreary, so I replaced the factory touchhole liner with a Chambers' "White Lightning"; MAJOR difference.)
(3) Lyman factory trigger set is... could be a heckuva lot better, but can be adjusted to a gnat's-hair letoff - which still doesn't do anything for the backslap, rough gritty guts, etc. (L&R makes a replacement set, in their "Deerslayer" line).
(4) The stock. Herein lies the rub, at least for me. The factory stock was comfortable for me, period.
There is, as longcruise says, room for personalization, but for me, the far greater issue than the (personally offensive) looks is the lay of the grain through the wrist: extremely weak: mine broke (long, embarrassing story... but it broke at a weak piece of grain). Therefore, my barrel and lock are gonna be getting a new stock soon, once I've decided just how much of the Lyman steel I'm going to be reusing and inletting.
(5) I did replace the triggerguard with one I built; didn't care for the look of theirs, and I wanted a little more room for a gloved hand (late elk season here in NV can be a little frosty).
And, (6) Personal choice here, but I do wish mine was a .54, which has nothing at all to do with your questions.
So, that's pretty much the pro's and con's I've found with my own.
