Harbor freight tools are just fine, if you know what to look for as far as quality. Personally, I picked my coolant system pressure tester from Amazon. It was a fairly cheap kit, something like $30. The hand pump it came with sucked, but I use the fittings, which are great quality, with compressed air and a regulator w/ a gauge. Just make sure you do not over pressurize the system, obviously.

If I had to guess, since the kit is buried away at the moment, I think it's an astro ai? I could very likely be wrong but it is a decent brand. I didn't care about the hand pump because I bought it to use with compressed air.

I would highly recommend using compressed air because you can literally set it and forget it. It will hold steady pressure on the system indefinitely and you can make small adjustments as needed.

Edit: Just went and looked it up, I got this one: https://www.amazon.com/dp/B003V9L05G/ref=cm_sw_r_cp_apa_i_JdjAFbF62TQM4