Quite a few members have used this on from Harbor Freight at $25 plus shipping. I bought for even less when it was on sale at one of their stores (you may have a store near you). However, I have never used it yet so I cannot comment on it. If I was you I would start another Thread and as who has used the Harbor Freight compression tester and the results.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93644
I cannot compare the Amazon one to the Harbor Freight one. They may even be the same kit made in the same place. The Harbor Freight Kit has an adapter to take the compression through the Glow Plug hole and also has an adapter to do the same by way of the Injector Hole.
Buying an used Engine is always a gamble. If the Engine will crank over you can get some sort of a compression reading from it even if it is laying on a pallet.
However, even if the milage the Seller is telling you is correct this does not tell you if the Engine was overheated or run without Oil due to something like an Oil Cooler Hose leaking or just plain abused by the prior owner.
I think the best way to buy a used Engine is the get a whole car with some other problem like a bad body, trashed interior or bad transmission. This way you can run the Engine and maybe even test drive it.
It is a problem to get rid of it afterwards but there is other parts you can salvage form a whole car.
If you buy a used Engine buy itself you would be best off getting it from a Salvage Yard that gives or allows you to buy a warraty on the Engine.
Buying from the salvage yard would cost more but if you buy from a private seller and the Engine is no good you will have 2 no good Engines on your hands.
Another thought is to "Buddy Up" with someone local to buy a complete Car. You need the Engine but someone else may need the other parts on the car.