The factory service manual tells you to check the compressing with the engine at operating temp. However, most people check it could simply for convince.
The cheaper diesel compression tester at Harbor Freight is $60. If you go to the Harbor Freight site, you can bring up the instruction pdf and there will be a page with what engines it will work on.
If it works this will take you to the pdf.
https://manuals.harborfreight.com/manuals/58000-58999/58801-193175446800.pdf
The older kits were not Maddox kits. People did occasionally have trouble with the older kits. The little valves are Schrader valves same as they are on tire valve stems. Those have been one source of the trouble people have. The other was the 90-degree attachment was in the old kits fragile.
A few believed the gauges were not accurate and acquired other gages for their kit.
If your engine is starting OK in cold weather, you are likely getting sufficient compression. What you are looking for with the compression test is if the readings are within the allowed compression balance between cylinders. And things like you have 2 adjacent cylinders that are low, but their compressions are similar which can be a leak between the head gasket of 2 adjacent cylinders and so on.