I've used the Chemseal products from Spruce with no problems, other than the usual sticky mess ones.
I think the key is simply to buy to the correct specification whoever the manufacturer is. From the PRC document -
Meets requirements of specifications AMS-S-8802 formerly MIL-S-8802,
We typically use type II, Class B, with the following number giving the working time in hours (usually 2).
Just buy to the specification, the Chemseal product meets the same spec.
PR1440
https://www.silmid.com/sealants/fuel-tank-sealants/ppg-pr1440b-2-aircraft-integral-fuel-tank-sealant-500ml-kit-ppg-dtd900-6138-msrr-9144/
Its twice as expensive as the stuff we used for 30 years (I think that was PR1412), but that has fallen foul of the REACH regulations.
Pete