I've bought a few multi-tools over the years and I have found they usually have either more than you need (needless weight) or not enough (pointless in an emergency). I've usually had to add bits and bobs to make up a proper emergency kit for a specific bike. I've given up buying them.
I carry a number of short Allen keys (checked against the fasteners on the bike, possibly only two), a small adjustable spanner and a small ratchet screwdriver with several bits hidden in the handle. All tied together with a rubber band or in a small bag, with patch kit and/or spare tube and levers. That will take care of most issues by the roadside, and it doesn't take up much room or weigh a lot. Further away from home, I take more (cable ties, gaffer tape, pliers, chain tool etc) but this is outside multi-tool territory anyway.
TL;DR: commercial multi-tools are an educated guess at what most people on most bikes need and are unlikely to be a perfect fit. Cheaper and better to knit your own.