I do not own one nor have I fired one, but I have seen a couple. The main reason I don't own one is I took the advice of the more experienced people on this forum, and I obviously have a great deal of respect for the talents of many of this forum's members. I just think that the denunciation of these things often goes to far. I simply wanted to point out that these dealers will proof test the guns, and they are not made to be wall hangers or only fired with blanks as many people have suggested. Recommended load information is included by the dealers. The varying degrees of quality I mentioned are mostly reported in terms of how good the bores are and whether the locks run well out of the box. Some of the dealers inspect this, the frizzen, breech plug, etc. before they ship each gun.
Here is a description from FlintlockRepair.com concerning the barrel strength:
"The steel in the barrels are typically SAE 1026 high pressure DOM (drawn over mandril) grade which is typical of smooth bore. Metallurgy of India musket barrels comply with modern and original requirements and have been shown to have a tinsel strength of approximately 85,000 psi."