You will like your commando Mark III.
The earlier ones are indeed nicer. They are all metal and wood and seem to be built a bit better.
I have been a fan for many years and can help you with your Commando. The firing pin is the weak link. There are several versions and a rather long history on this firearm.
The earlier ones are built using grease gun mags, which now go for about 25.00 each. Used to be you couldn't give them away.
The later ones are Thompson mags because the manufacturer found a source for them in England for pennies each.
You have to modify some Grease gun mags by cutting the notch to hold them. Some grease gun mags don't have the notch. It is easy to do, and I'll post pics when i get the chance.
We used to have a long and very informative link on Gunboards for this weapon which appears to have been removed during their upgrade.
Here are a couple pics of my Commandos. One is a standard Mark III, the other is the earlier "open bolt" model made with actual grease gun parts.
I also have detailed machinist drawings for all the internals should you need them.