Firstly I can say Jump Start is 100% not a gimmick. It helped my pied male's life when he was off feed and sustained a nasty belly burn plus the systemic infection that sometimes follows. He was off food since April and only took his first meal this month. If not for the caloric/vitamin boost I have no doubt he would have passed.

Unless your snake has substantial weight loss, i.e. you are genuinely concerned they may die, don't use it. This stuff can't really be dissolved in water (it is almost pure fat and sugars) and it is best injected into the mouth with the supplied plunger. There is enough length to get it down the throat just a little without worrying about the windpipe. Let your snake drink afterward. This stuff is very thick and if he tries to regurgitate it will get stuck in the mouth and cause a whole mess of problems.

Good luck, I hope your snake recovers soon!