Here's a take on this...

My partner finds various gu's don't sit so well in his stomach. He also has difficulty getting them open due to a hand injury which can mean keeping a tight grip on small things is very tricky.

So we tried honey in one of his water bottles, several tablespoons well diluted with water. Too sickly.

So we tried glucose. This works a treat. I put 5 heaped teaspoons of glucose (powder) in one of his water bottles when he is going on one of his long training rides (he usually does at least 1, but often 2, 100km+ rides per week - for example, on Sunday he did 130kms, on Tuesday he did aboput 110kms). The glucose is barely noticable in flavour but gives him the energy he needs to get home.

So he takes a bottle of plain water, and a bottle of glucose water, and a couple of 'bike bars' to eat. He usually stops at a school somewhere to top up his water bottle, and reserves the glucose bottle for the last leg home.

He also uses the same combination on 50-60km races because it is impossible to eat at the pace that is set (usually ending up with a 40km+average). So he takes two bottles and starts the glucose bottle about half-way through the race.

He finds the glucose water provides almost instant energy and is easy on his stomach.