I have to admit to being slightly baffled by their descriptions of "Normal THD" and "Low THD". Both are electronic ballast with THD under 10% which is low enough that you basically don't have to worry about it.

They do have different circuits which you may find important. Series circuits have all four tubes wired together in a line, so if one of them goes out (or is removed) then they all go out. Parallel circuits wire each tube separately and if one goes out then the others keep working. Remember that there are good reasons for not wanting to keep pumping power into a failed tube but there are also obvious benefits.

Another difference is the starting method. One appears to be a straightforward instant start which just blasts the tubes with a very high voltage to kick them into life, which does tend to shorten their lives if they are frequently switch. The other is described as ProStart which is probabyl their term for Programmed Start which controls the initial voltage much more carefully and so prolongs tube life when it is switched on and off frequently. Not a showstopper either way for growing plants since the lights are usually only switched once per day, but programmed start is better if you don't have to pay through the nose for it.

Perhaps the most important thing from your point of view is the ballast factor. 0.88 means that these ballasts will produce only 88% of the rated lumens shown in the tube specs. This has become almost a standard for commercial lighting because it produces roughly the same output from a new 32W T8 as you used to get from an old 40W T12, hence making retro-fits very easy and very efficient at saving electricity. If you want to overdrive then there is no real problem, you'll get maybe 30% above rated lumens instead of 50% but you'll be closer to the most efficient range of the tubes. If you want to run four tubes off the ballast then look for one with a higher ballast factor, close to 1 or even higher than 1.