I have not installed the check valves in my pump because it seems the unit has adequate pressure. I will retain them as spares but they appear to fill my needs well.
My only objection was I thought all the parts ordered were in stock and ready for shipment however after several days with shipping notification, I checked again and found the items had been back-ordered and shipment was delayed. Had I known this initially, I might have shopped around to find parts in stock that could ship sooner.
I have bought from Jack's previously and find they have good service and value, which is why I used them again.