If by holster you mean gun holster, then you might want to consider a machine that can use 207 to 346 thread. I looked into machines a few months ago. (bought an Artisan Toro 3200...similar to Cobra class 4) And one major thing was the flat bed machines max thread was usually 138 or 207 on top, and 138 bottom. This is fine for thin items, like wallets, cases, and purses. But, not really ideal, if you want to make holsters or anything heavy duty....Though, maybe its personal preference, I like using 277 thread for anything above 8-9oz leather. And use 277 - 138 for wallets.
Also, as mentioned above, many flat bed machines won't clear 3/4"... some won't clear 1/2".
The Cobra class 4 and Artisan toro 3200 have really great range of thread options and are more versatile (when I went to Artisan store, they had a 1in thick piece of leather in the machine for demo). But they definitely cost more than a flat bed machine.