Before I figured out the inline temp probe, I would constantly pull the hose out of the carboy and hold the thermometer in the stream to make sure the temp wasn't creeping up or down. Most people that go to an external chiller setup do so for one pass chilling. If you're going to recirc back to the kettle, I actually think an IC is the better choice.
I'm bringing this thread back to life because a while back I bought a 40 plate chiller from someone on HBT that's one of the short ones. Not the elongated one with more surface area that Bobby sells and would love to have....damnit.
At any rate it's got the 1/2 hose attachment's for the water in and out and the 1/2 barbs for the wort (barbs aren't removable). Because of this my questions is for checking the wort temp am I stuck with using the blichmann thrumometer? Like Bobby said above, I only want to do one pass otherwise might as well go IC.