I think of the GPR a little differently..... I have shot an old GPR for years & it is still all original & I have shot over 5000 rounds thru it. Still original frizzen & lock & trigger & I have never had a problem with it. No it is not fancy, the lock is not as good as a Chambers, L&R or a lock built buy a company that bases if livelyhood on Locks..... And no the trigger is not smooth a Timney trigger.....
You have to accept it for what it is... it is a $300 rifle. Comparing it's lock to a $100. L&R, Siler, Chambers Siler, or any other lock is not a just comparison... Like comparing a small garden tractor to a 4000 Ford for plowing 100 acres... If the rifle had a lock that was as good as a Chambers, barrel as good as Getz, trigger good as Timney, it would be a $900 rifle instead of a $300 rifle.
IMHO, It is a $ 300. rifle & it is what it is.... I still think it is the Best Buy for the Money in a low priced mass produced rifle.
Also, if you take care of it & sell it later, you will have much less loss of $ compared to the T/C, Pedersoli, etc. from what I have seen on the used market & a used Lyman Flintlock will sell imediately if it is priced reasonably & taken care of.