Finally I tried Flex Shot. It was very easy to use compared to even a nice no drip caulk gun (they still ooze out after you stop trigger, just not enough to drip, so material waste). Very easy to control the Flex Shot and I really liked the way you seal the tip after use. Just let a little sealant out the top maybe 1/4" and let it cure. To reopen just pull this plug out. Much better than how I seal a common caulk gun, nail in tip hole and then wrap with kitchen film and put rubber band around, not really effective seal, material goes bad inside caulk tube.
I also really like that Flex Shot is supposed to be somewhat tolerant of a little moisture on the surface being sealed silicone is not.
However, I do not like the Flex Shot website at all. Lots of marketing hype and hard to check out without them trying to load you up with other stuff. I accidently bought a can of Flex Seal I didn't want and they said unless I paid extra it could take up to four weeks before they even ship the product. Yuck.
Keep in mind Flex Shot is not paintable and water does not clean it off your fingers. Overall I like Flex Shot and it is flexible enough to solve the gap problem with my tube. It does cost quite a bit more than regular silicone in tubes.
Bottom Line: Yes, I would recommend this to a friend