I liked it. I jumped on the 300 blackout band wagon when the round came out because no one made a reliable 7.62x39 AR, or there was a million year wait to get one, so the easy alternative, and cheap since 90% of the gun is the same as a 223 gun and I just had to change the barrel. Like the guys said above, make the brass from 223 brass, and I bought H110 powder and military pulled 147 gr bullets to shoot. I never took it past 300 yards, but it was awesome to shoot at that distance, didnt have a ton of recoil, it was super accurate, and after getting your brass done it really isnt much more than 223 to reload.
Best part is all your 223 mags work for it and if you ever decide you hate it, just toss a 223 barrel back on it and sell the .300 barrel.
All that being said, when everything started to happen with shortages, I went back to just 223 and 308 for my rifle calibers since I really didnt need an intermediate round and reloading supplies became non existent. If you dont reload, this is a bad round to get into due to the cost of factory ammo and how hard it is to find it... but if you want something with greater effectiveness inside 200-300 yards than 223, its a neat round that can be reloaded cheap.