I'll mostly say what I said on my SHPR2B P-Rail Hot, whick I have on the bridge: It's a great addition... Basically if I knew better I would just get an even cheaper guitar probably (that would have of course a comfortable fretboard to play and good looks) and just change the electronics-pickups. Ready to go!
So, the pickup is great!!!! I have it with a 3-position switch on the right of the bridge. With the SHPR2B also on the bridge you can play virtually ANYTHING!!! The single-coil is convincing and clears it up for strumming and clearer tones or funk (ok it's not becoming a tele, but still), the P90 gives it some extra spunk while retaining clarity, and you have a fat tone with the humbucker when you need extra beef!! So, my reccomendation to conclude: try a guitar with P90s. You think you need that tone? Buy it. You are ok without it? Go buy something cheaper, but certainly with a coil-split... It opens up so many possibilities..
To be frank though, I don't use the P90 on the neck nearly as much as on the bridge. Think if you need it or if you could settle with a coil-split only.