Bought this on Amazon along with the Romeo 1 pro for my new M18. Fit super snug and dialing in the red dot and bore sight took 2 seconds. Haven't had a chance to get to the range yet but was surprised how far off the red dot was from the bore sight going from say 10 feet to 21 paces (about 60 ft. Have a long hallway in house). Interested to see how accurate it is.
https://www.amazon.com/MidTen-Sight-Boresighter-Gauge-Batteries/dp/B07GGWJSJ6
I haven't tried it on my XL yet, but did the job on an AR-9. Priced right, too.