Sikaflex makes a good product. I have not personally used it, but I see it in use on some quality boats and it seems to do very well. Personally (and that being a big part of this), I've gotten used to the Boat Life products over the last 2 decades and haven't really found a need for anything else (this also includes the marina where I work - it's pretty much what every tech uses). LifeCaulk IS a stronger, longer-lasting product than LifeSeal, but Lifeseal is more versatile and has more adhesive properties than silicone (which generally is considered to not be an adhesive) for those times when that is what is needed. Lifeseal tends to resist mold and dirt better than silicone, as well.
Now, none of this means that I'm saying the use of silicone is a bad idea - far from it. It's just that it's an old technology and there have been improvements made over the years. HOWEVER, in an area where a "sealant" is the primary property needed and a spot where you plan on removing the piece on a regular basis to inspect, I think it does make a lot of sense to use silicone given the cost difference. Not that a tube of LifeSeal or Sikaflex is "expensive" in comparison to how long it lasts... or boat ownership in general!... but it could be seen as overkill by some to use a more expensive product on a short-term use area.
Personally (again - "personally") I like just having to have one or two different products lying around for all sealing and/or adhesive needs. Those being the two BL products. It's also nice to know that I don't have to worry about a surprise rain ruining the sealing work that I just did. As Seasick mentioned, the two BL products, for example, can be used in the presence of water. Here's a quick story about that (although I may have already shared this and forgotten!)... 'Bout 10 years ago, at home, I was inspecting the flashing around my chimney cap. I realized it was pretty much gone - cracked and deteriorated. I only had a little bit of LifeSeal left so I ran to the local HD store and bought their best sealant (some type of silicone). I used up what LifeSeal I had left, then finished with the silicone. Less than an hour later, we got a BIG rainstorm. The next day I went back on the roof to re-inspect and the LS was completely intact... the silicone was completely gone. Again, this is not to say that silicone is bad - it's just that it cemented the reason why I like the BL products so much.
LifeSeal does come in a "cameo" color that is an off-white, but I have never used it in person. My Grady's deck is gray, fyi.