In a past posting (Simple versus cheap) here:

The text focused on the lack of high level finish in simple guns. Recently I bumped into a page on the Faeton underhammer muzzle loader. It is a simple action, arguably the simplest found in a firearm. The action comprises four parts: the hammer, trigger-sear, trigger spring, main spring which also functions as the trigger guard. These four parts are housed in a surprisingly simple unitary action body. Just two axles hold the four action parts to the body.

The Faeton is not the only underhammer muzzle loader. Other makers had made muzzle loading long arms and pistols on this simple action. The difference is that the Faeton has been made at a very high standard. The maker, Roger Renner, has chosen to go the best quality route on tese simple guns. It is probably the only instance where a simple design has been made at the highest standard, equal to best gun standards. Personally I find the result stunning. It is a unique combination of simplicity and quality that shows what can be achieved when functional simplicity is combined with top grade finish.

More on the Faeton can be found in the maker’s blog:

the opening photo is also from this site.