If using it for varmints past 100, a scope. 2-7X or compact 3-9X.
Since yours is a folder I'd continue to take advantage of the compact size and go w a 2 moa reddot on scout rail.............Aimpoint PRO type or maybe a micro.
Had a PRO clone on my AR, found it too big.
Liked it on my Contender handgun though.