Hello. I'm new to the forum. I'm looking for a conversion like the Ciener or CMMG for my S&W M&P15X, so I can practice with rimfire ammo as well as the fact that I enjoy ammo interchangability between multiple arms for versitility in my bug out bag. I'm not interested in buying a separate .22 rifle for this purpose, as I dont want to carry two rifles through the bush. I'm going to try to find a deal on a second hand unit that someone is no longer using, but I want to know if there are any specific brands or models that I should avoid? I don't want to accidentally buy one with a known bad reputation. I would like to be sure to get the best unit I can, but have read conflicting info on who makes the best one and what the difference in options is. Can you advise?