I have not used them but they are Flatlander racing and I've seen the product for sale before. Bear in mind the pisture is not thier shortblock but an MP which includes the cam, timing set, lifters, and timing cover. It is not a fantastic deal price wise. But, they are doing what should be done, and using good parts. The cast 4" cranks can hold close to 600hp when built properly and I've buitl two that make over 700 with the NO2 on them. (Not that I'd recommend that...lol. It wasnt part of the original spec...) A comparable shortblock that I do costs about $200 more assembled but that's with main studs and oiling system work and a set of Eagle H beams. Not the SIR I beams they show.