Well, the stuff that you link to, McNett Seam Grip, is for urethane coated fabric, not silicone coated. For Silnylon you need this stuff, Silnet.
https://www.theepicentre.co.uk/item/Mcnett/Silnet/6PC
So a tube of 28g Silnet is plenty to do several tarps, BUT, £8 + £5 postage!, and only enough that you will want to use if for that purpose, vs (for instance) Screwfix No Nonsense Builders Silicone 310ml for £5 and available to collect, and can be used for other sealing jobs around the home.
Furthermore, and this is important,
Silnet has a very definite shelf life, cure time increases with age. I bought some, did a tarp, put it away for a year or two, wanted to use it on another tarp and was pleasantly surprised that it had not set in the tube. Great. This was last summer, hot, dry, windy weather, perfect for drying stuff. Pitched tarp in garden, applied sealant, and waited..and waited. 6 hours later, sealant showing NO signs of drying!!! I was able to clean it all off again using acetone, and went and bought some builder's sealant.
I did a little sample piece to test and contacted McNett USA and EU. It took over 48 hours for the old Silnet to become touch dry! News from the manufacturer is that this is the effect of age, sealant is still wet, no detectable change from good/new, but cure time becomes progressively longer. They have had some sent back that had sat on a store shelf too long and behaved this way the first time it was applied.
McNett Seam Grip, the urethane stuff, does set in the tube, so you may not get to use a whole tube, but at least you will know before starting the job.
If all you can find is the high modulus builder silicone, the Silnet probably will perform better, once cured, but it does have that down side with cost/quantity/shelf life.