Multi-Tools are single hand held devices that put together different sizes & types of tools. A simple multi-tool will contain various hex or allen key sizings alongside a flat & philips style screwdriver. These are perfect for simple tightening or gear/brake adjustments. However if you feel you would like a multi-tool that will give you wide range of tools for any situation then you need a multi-tool which has, hex or allen keys, torx keys, screw bits, tyre lever & a chain splitter. Having this tool (and knowing how to use it) can be the difference between making that ackward call home for a lift or limping home wih a useable bike! Another variable consider is weight. As your multi-tool becomes more complex it also, in the majority of cases, becomes heavier. If you want the maximum number of tools on your device but with too much of a weight penalty then have a look at The carbon range from Lezyne.
We stock multi-tools from BBB, Lezyne & Birzman.