I have a SPAS-12. They're right. It's a collector gun that isn't practical as a combat shotgun. If you just want one as a toy/collectible, then sure. It's fun and and always attracts attention. They also feature one of the most comfortable folding shotgun stocks. The only time mine malfunctions is when the shells are too weak to cycle it. As noted in the manual, it needs hot loads to function in semi-auto. If you really desire a pump/semi convertible, then the Benelli M3 is the way to go. There's really no point to one though. Benelli M1's are cheap, cycle much more reliably (with lighter loads), and it's easy to reach the op handle and cycle it manually. Also easy to find Surefire fore ends for it. There are none available for the M3.
The M4 is nice, but a used M1 is a way better deal. The only advantage with the M4 is the ability to attach heavy accessories to it without affecting reliability. Most people don't need that ability, and you pay dearly for it in both weight and money. That said, the M4 Entry 14" with c-stock is badass as hell.
Also consider the VEPR-12 while browsing badass shotguns. Sometimes the QC is spotty, but any problems with them can be remedied, and they come with a warranty. They make an awesome SBS.
I played with a TP9 briefly. They have a long spongy trigger. I thought about trying one as a PDW, but now that the
USW is out, I'm more interested in that. The trigger will be like a CZ75 trigger.