I own one but it's honestly not super useful for tuning a CRT.... it's missing the nice gradiant patterns that are necessary for dialing in the Red Green and Blue gain and cut-offs. I also found that the few times I did tune on the TPG once I put a real board in there I had to re-tune because it just looked different.
it's a great tool for testing if a monitor is working properly particularly if the cab is missing or has a non-working PSU or doesn't have a JAMMA harness, but I wouldn't use it for tuning.