Many barnds just make their own tank (or buy what's available) and build their own "saddle" for it to ride in/on. From there, they all use generic parts to complete the package. In MOST cases, Tee-Jet components are used.
Any reasonable priced sprayer will do. After getting it, the "bells and whistles" can be added. I used a Fimco (TSC) sprayer as a base, then added 10 PSI check valve nozzle bodies, better pressure guage, a hand wand kit, and a Hypro 5 roller PTO pump. In all, I have around $650 invested in what is as good of a sprayer as any more expensive 65 gallon models.
I prefer the PTO pump myself. In some cases, I spray mixtures that require higher delivery rates than I suspect the electric pumps can muster. (higher delivery pressure)
If you don't maintain (read; CLEAN) a PTO pump after using, it will not last. (Same thing no doubt applies to elect. pump) If you tend to slack off on that sort of thing, the electric pump is cheaper.
I prefer a 3-point model to a trailer. Just a personal choice. I can see the advantages of a trailer type for "group use".