Glycerol in a pure form is a liquid.
To make Glycerol in a capsule form, you must make it in a powder form to be encapsulated. To do this, the percentage of active has to be lowered since in pure form its a liquid. Hence the 65%.
If you're simply looking for grams of Glycerol, the liquid is going to provide higher dosing - but you don't necessarily need that high of dosing of Glycerol for it to be effective. Liquid glycerol is actually extremely cheap as a raw material, so you're seeing brands compete and promote higher dosages than is necessary.
Some people think it's new, but its actually been around since the old Twinlab Glycerol Fuel back in the 90's. The upside is higher dosages, the downside is the inconvenience of a liquid and that it hurts some people's stomachs. (I tried it back in the 90's and it hurt my stomach then. When it started getting popular again last year, I tried it again and it bothered my stomach even more than I remembered.)
If you look at the original powdered Glycerol Monostearate products, people loved some of the original ones and the dosage was 6 grams and GMS was only 10% to 25% actual Glycerol, so 600 mg. to 1,500 mg.
GlycerPump is 65% so it provides a lot higher active % than Glycerol Monostearate (GMS).
The GlycerPump write up gives a lot of information on the subject for anyone that wants to read up on it:
https://seriousnutritionsolutions.com/product/glycerpump-120-caps/