I'm really surprised their MP5 didn't take off, as it's a pretty popular first world law enforcement weapon.
But then, look at the price of 9mm with a government agency discount.... You can buy a lot of ammo for the cost of a TW5
The next best option might be the UMP, but even then police agencies typically only buy the UMP in .45 to supplement the MP5....
You could buy an arsenal of AK's and a lifetime supply of ammo for the cost of an AK PTW, and if you're using an AK, chances are it would be beneficial to the rest of the world if you did not receive any training....
The HK416 trains like an M4
The 468 and IAR (colt or the 416 doesn't matter) both train like M4s
Maybe the G36 actually, it's current service, widespread use, used by police in various countries, very popular.
I'd say it's either the G36 or they get into making GBB pistols lol