On our trip to Spain I decided to use the Zefal Z-Console pack that sits neatly on the bicycle top tube behind the stem. It looked like an ideal solution for items that I needed access to quickly and as it had a handy cable in/out hole, it would enable me to charge my phone via my dynamo hub on the go.
While very handy for accessing money and glasses in practice it wasn’t great for using the phone. Being behind the stem of the bike I needed to look down straining my neck to view the screen which seemed further back then felt comfortable. Also the plastic cover reflected sunlight and using the touch screen behind the plastic was fairly hopeless.
In the end each time I wanted to use the phone, for example to look at Google maps, I had to unzip the bag and take the phone out which 90% of the time meant stopping.
In conclusion the bag is very useful for quick access to items but not so good for phone use.