I use the Infinicon as well. I paid $150 a few years ago. You can't get it within 10 ft. of a good R22 leak, it freaks out. Not as responsive to 410. It worked well with 134A. You have to replace the little sensor thing every 2 years or so. I think it costs $40.
I got mine off Ebay. Its an Inficon TeK Mate. Works pretty well.
I have only used it a few times. I prefer compressed nitrogen and soap bubbles. If you can't find it with nitro......you probably won't be able to find it with electronics.
Microleaks. You get on a roof in the howling wind, and other calls waiting and just may find that an electronic works better. I had a copper-to-steel joint that had microleaks, barely would make a cocoon.
But my inficon (the more expensive one, like $310 usually like 325-350) picked it up instantly.
And you can charge more if you start calling the bubbles "leak reactant"
I still use the tried and true johnson controls hg10 formerly made by GE it picks up a leak as small as 1/2 ounce per year. The down side is that it requires a120vac source to plug it in and the cost its about $400. That and the sensors like to go up often