I have the micro in .223 and it has been 100% reliable. Small and fast handling. Mine is an older one with the original tube stock. I think it would be perfect in 6.8 spc or 300 BO as the .223 looses a lot of energy from the short barrel, but it was the authorized caliber were I used to work.
If you are looking to suppress, make sure you can find a suppressor for the 7.5 inch barrel. I haven't been able to find one that I was convinced would live long on that short of a barrel in .223.