I haven't shot one but gave one a very close examination thanks to a local dealer friend. IMHO it's about as useless a device as I can imagine. Changing from rifle to shotgun is not easy, the piece is cumbersome and heavy and hard to operate. Woe betide the officer who made a mistake in his selection in the heat of the moment. Having both shotgun and rifle operate off the same trigger seems like a recipe for disaster.
If you need this combo (and you probably don't) the set up I thought made sense was the chopped Remington 11/87 attached to the foreend of an AR-15 (similar to the M203 grenade launcher).