What Compression Tester to Get

That tester is fine, but I wouldn't get those fittings. They're a PITA trying to get them in and out and not leak. Use one like below. Decades ago they didn't have these so I made my own out of a spark plug and a 6" piece of pipe.  You want the 12mm.

https://www.aircraftspruce.com/catalog/topages/atscompressiontester.php?clickkey=4690

Hi Shaun,

Unless you are offering a professional service ie this is for your own routine (100 hr service) engine management the cheap (there are identical cheaper automotive units) tester will do just fine.

The main objective of compression and leak down tests, is to establish bench mark data (usually from the first 100-200 hrs). All future test will be compared against the bench mark & subsequent tests, to give you an idea of your engines "health" 

Using the same devise (your own) for each test, enhances the value of the data, even if the tester itself is not so accurate, as long as it gives consistent readings.

Note: Rogers advise regarding spark plug/tester access.

😈

I like the ones here:https://www.aircraft-tool.com/detail?id=2EM

They are half the price of Aircraft Spruce.  They also sell the 12 MM adaptors you need for the plug holes.  

Cheers

Even cheaper if you get an automotive one.

There is nothing special about an aircraft engine, that justifies the prices demanded by aviation suppliers. The engine want know/care what sort of leak down /compression tester you use.

If you are only using this devise every 100 hrs, either borrow or get a cheepo.

In this test, accuracy comes a distant second to consistency.😈

You can use one of the testers you found or were recommended, but as Roger mentioned, you'll need an adapter for the spark plug inlet.
I bought the following product.
https://www.temu.com/-automotive-cylinder-leak-down-tester-kit-gasoline-engine-compression-dual-gauge-leakdown-detector-tool-set-for-pressure-check-leakage-rate-test-with-extension-rod-g-601099620983085.html
The orifice in this test unit and the gauges on it aren't suitable for Rotax. Toss the test unit. The hoses and adapters are cheap and work great.

If you can manage it, put a 3mm long orifice with a 1mm hole inside the block and replace the gauges on it with two 6 bar or 100 psi gauges, then you can also use the tester that came from Temu. The cheapest solution... I bought them for many of my friends and modified them. They are all using without any problems.