I've experimented with gels before, as I do a fair bit of intense training, most of them are very chemical-like and unpleasant to swallow.
I purchased some samples of carb-boom, just to see if I can enhance my performance during training.
For effectiveness I give this gel 5/5... also, for taste, it gets a 5/5 for being the most 'real-tasting' gel out there. It's very easy to swallow and doesn't upset the stomach like other gels seem to.
4/5 this time as I'm reviewing the Double-espresso gel, which contains 100mg caffeine. Taste-wise, it tastes very realistically of coffee, slightly sweet coffee actually! I tried this during a 3hr exercise session, when I hadn't been able to eat beforehand. 20 minutes after consuming this, I was high as a kite and had energy to burn... not only did I whizz through my spinning class on high-resistance, at speed (Having just done an intense workout class + weights beforehand), I went swimming afterwards and zipped 80 lengths in a shade over 30 minutes.
I highly recommend this particular gel if you're in need of a serious energy boost and mental perk!! I don't recommend it if you're sensitive to caffeine!
