Brand new to the air gun world, purchased a 22 and 25 pcp from a friend, have a scuba tank, refills not real handy. From lurking on here appears Yong Heng compressor is my low cost option for refill. But confused in differences between, Simple, hardcover etc. units. I do not plan on shooting a bunch, less than 100 shots a month. I can watch pump and go slow. Will the simple unit do the job or should I spend more for a upgrade or ???? Thanks