The Lancer Shotgun Barrel Extension Clamps are designed to work with LSX extension tubes. Unfortunately, there is not an LSX extension tube available for the Maverick 88.
Yes. As long as you are using the LSX shotgun tube extension on your Benelli, the Lancer Shotgun Barrel Extension Clamps will fit. You can find the shotgun tube extension for Benelli Shotguns here:
https://www.opticsplanet.com/lancer-benelli-m1-m2-magazine-extension.html
Yes. If you have the LSX extension tube equipped to your Remington 870, then the Lancer Shotgun Barrel Extension Clamp will fit and function as intended.
Yes. The Lancer Shotgun Barrel Extension Clamps will fit and function as long as you are using the LSX shotgun extension tube for the Mossberg platform. You can find the extension tube for your shotgun using the following link:
https://www.opticsplanet.com/lancer-mossberg-590-930-magazine-extension.html
The Lancer Shotgun Barrel Extension Clamps are Height: 2.25 in. and Width: 1.75 in. (tapering to 1.5″ at the ends)
This product is designed for use with the Lancer Shotgun Extension Tubes (LSX).
The Beretta 1301 Competition Lancer.LSX Shotgun Extension Tubes are located here, in Plus 2, 3, 4, 5 and 6 models:
https://www.opticsplanet.com/lancer-beretta-1301-competition-extension-tube.html
Mark H.