Why not try talking to Sika? I hope you have a better experience that I did, Customer Services (ha ha) totally ignoring emails on their own mail system - if their customer service is so bad, can their products be relied upon?
Ive used both ,on deck sealing hatch frames.The EBT version seems to be more prone to deteriorate with UV and weathering.(3 years) .Ive currently had more success with CT1, (so far.)
I used 291 to seal under a rubber fender strip right along the hull. It seemed to have very little adhesion and was easily rubbed away with a finger end several weeks after it should have cured. I have not found the modern Sikkas to be anyway near as tough as the Sikkas of several years ago. I now have used CT1 on a number of applications and I am very pleased with that but it is not widely available.