I have used it for a few years now and I also use immune boost, also just ordered the missus some gut endurance to try out. If you want to know what it does have a look at the website but it's basically a recovery aid and lactic buffer, claiming to reduce lactic acid and enable you to train longer and harder.
It's also pretty hard to prove outside of lab testing so you either believe it or not. Thing is when you aren't using it you are training less and visa versa.
I feel it works for me and have done my own basic tests around harder efforts when taking and not but you need to be taking for a few weeks I think before it works so the pain subsides !! I will find out after this weekends marathon.
The Pirates get a good 25% off so maybe worth a try.
As for feeling worse, get it out of your system and try again in a few weeks, if it happens again. I would steer clear and email them, I am sure they would be interested in your reaction.
In the meantime have a read here http://triathlete-europe.competitor.com/2015/02/12/tried-tested-xendurance
I know, I was doing a search on race reports and this came up, can't beleove we were looking at this and it never came to anything. Just wanted a UK perspective on the full distance. Looks like a great place to spend a few weeks so if you have any tips on places to go and with 2 kids that would be appreciated as well