Probably the best $249 I've spent from the gun budget in recent years, turned a 2006 paperweight (basically full of lead/carbon) into my current favorite rimfire can. It is silly quiet and allows me to use it on my SMG and my 22 WMR. Win, win, win. I posted a long winded response to the same question from someone else, I've copied it below.
I had an original sealed Outback 2 purchased in late 2006 (took possession January 2007) as my first silencer. I loved that thing with thousands and thousands of rounds. I didn't really keep track exactly how much went through it but it was, conservatively, north of 6,000 rounds (~80% rifle). It was never cleaned using any sort of soak. Around 2010 it became sufficiently loud that I stopped using it entirely so it sat in a box in my safe. My AAC Prodigy effectively became my only rimfire can for several years. I missed out on the original upgrade program they offered where you could pick your own baffle material, glad I did as this latest upgrade turned out better IMHO. As soon as the IOU program was offered I jumped on board because of all the new capabilities it conferred, most importantly the ability to service it by the owner. The IOU upgrade also permitted me to use it on my then go-to rifle, a ruger 77/22 mag, and my M11/9 SMG w/ Lage 22 kit.
My IOU upgraded Outback 2 sounds great on everything I've used it on so far, Ruger 10/22, Walther P22, and various rimfire ARs including a belt-fed Razorback. I can hardly describe how much fun it is to shoot steel plates at 200 yd with a suppressed belt-fed 22 and iron sights I may be less sensitive to FRP than others, but when shooting my IOU OB2 against my brother's Spectre 2 on P22s back to back, I could not tell much difference. Neither could my brother or the third party observer listening from 10 yd away w/o knowledge of which was being fired when. Of my hosts so far, the 22 mag bolt gun is probably the most impressive to me. Out in the open, the combination is silly quiet compared to what I am used to the 22 mag sounding like. Again, it sounds excellent on everything I've tried and is just stupid lightweight. Taking it apart is super easy, but I always loosen and re-tighten the core after shooting due to experience with my AAC Prodigy. Also, once you clue in to the fact that servicing the core doesn't mean it needs to be spotless, cleaning is easy too. I pull out the core, knock it a few times on the work bench, brush out the bigger crap, brush out the tube, add a dab of grease to the internal threads, and reassemble. Also, I would like to buy a beer for whoever it was at Gemtech that decided to integrate the 1/4" drive feature into the IOU/GM22 core. For me, the $249 allowed me to transform what had become a government regulated paperweight back into a star performing multi-role user-serviceable silencer. I have had zero problems with the core loosening from the tube which I read another user had experienced. I have absolutely no complaints about this upgrade, if I had 10 more OB2s I would have upgraded them all and not batted an eye after seeing how effective it was. I believe someone from Gemtech also mentioned that, at that time (late 2014/ early 2015) the IOU core going into the upgrades was slightly quieter than the GM22. I may have to look for that post but I am 95% certain. That is also great