I don't own one, so I couldn't tell you what pump they use. I know people that own them always rave about it, so it must be good, but in the end it's a pump on a cart with a spray wand. Not hard to do something similar, or nearly as expensive.
To some it's not about the expense, it will pay for itself. Time is money, so for some, sourcing the parts and building their own is more costly than just purchasing one that is ready to go out of the box.
I don't think you could go wrong buying one. It's purpose built, and very well built at that, so the choice is really up to you.