Since you said Hot Rails, I'll assume you mean an actual Hot Rails rather than "single-sized humbucker".
It won't sound as fat as a typical higher output humbucker like a JB, but it will be fatter than a typical single coil since it's reading a larger portion of the string. That said, it has a ton of output and really slam the front end of your amp. It's actually much hotter than any PAF-style humbucker...right up there with the JB, Distortion, etc. Tonally it kind of has it's own thing going...very aggressive and mid-focused. It's not a sweet sounding pickup at all and won't retain much of a true Tele tone...you'll have a fire-breathing hot-rod Tele on your hands. Clean tones are strong but not very pretty, but I've heard they can be if you split the pickup (I've never done this so I can't comment from experience).
It's also not likely to balance very well with a typical Tele neck pickup, but that can actually be cool under certain circumstances. I have one in a Strat where I use the neck and neck/middle setting for clean rhythm tones and slap it over to the bridge for aggressive leads...it's almost like kicking on an overdrive pedal.