Im getting a vt 625 kit in a few months ,want to play around with a meth kit as well.
Ive been looking into aqua mist's HFS-3 model, pretty much a good whole round meth system, included with a gauge, flow sensor and all the business, very good price too.
It uses a PWM system as well unlike the PPS systems with SP's, labonte etc.
Just so you know if you wanted to go down the route of doing a vishnu meth kit, look into AM's as they supply all the hardware for Vishnu and include items that don't come with vishnu's too.
Hope this helps a bit!
ill be making a thread when I've done the above anyway.