Solid rollers are bad on the street. Low RPM (idle/cruise) does not get enough
oil into/out of the needle roller in the wheel to cool the needles. The needles overheat and begin to spall material under load. The HIPPO lifters have an EDM passage that directs pressurized
oil at the needles and keeps them a lot cooler. Even then, they have a more limited life than hydraulic rollers. I have had Crane hyd rollers in one engine for 20 years (no exageration) with not one issue. The hyd rollers last longer. The hyd rollers in my 10.5:1 CR 540cid engine produce 700 HP and 700 TQ - hyd rollers really work.