S! Caps are 100% electrolytes. Each S Cap provides 341mg per capsule.

As far as GU replacement, I do use GU/or Shot Blocks on any run over 3 hours. You have to. Its funny you say replacement because I do use Vespa but I dont think I have ever mentioned it on this site.

Lots of ultra runners that eat low carb do use Vespa. Vespa allows you to consume less GU(any gel) during long runs once you have become fat adapted on a low carb diet. So, instead of consuming a gel every 1/2 hour, Vespa allows you to go much longer before having to consume one to carry on. But, Vespa is not a replacement for GU.

But, training on low carb and running over 18hours a week has taught me that my salt consumption and hydration must be spot on.