Product review (5 stars): Low price for a great gadget.
I wanted to be able to attempt to service my RV sealed unit and I still might, but I have determined that it is too expensive to try to keep it running when it is already over 12 years old and uses R22. So I am going to replace both with fancy new units.

This device was easily installed on the low side. It was too small for the pipe, but I connected it to the stub 1/4" pipe that they had used to initially fill it. It worked as described - no leaks and I was able to measure the static pressure. It was a little low, but I didn't have any R22 to add - I might use it to play with after I get the new ones installed.