I see threads on GJ quite often, where people are in immediate need of a 7mm or a 9mm hex as well. Lots of sets don't include those sizes. I think everyone should pick up a Bondhus 12195 metric L wrench set just in case. It's only $12, the L wrenches are made out of good quality steel, and the set includes the harder to find sizes of 3.5mm, 4.5mm, 5.5mm, 7mm, and 9mm.
While you're at it, buy an 11mm L wrench as well for $6 more.
I got tired of encountering hex fasteners I didn't have the right tool for, so I ended up selling off the multiple sets I had originally accumulated and instead bought everything I wanted in the exact form I prefer. I now have every size up to 22mm and 7/8".
-Sizes up to 6mm and 1/4" I have in L wrench (Bondhus), insert bit (Wiha), and power bit (Wiha) form
-Commonly used larger sizes from 6mm to 22mm and 1/4" to 7/8" I have in L wrench (Bondhus) and bit socket (Proto) form
-Rarely used larger sizes like 11/16", 13/16", 15mm, 16mm, 18mm, 20mm, and 21mm I have only in 1/2" drive bit socket form (Titan). Most brands don't make these sizes in L wrenches at all. I usually only encounter one of the larger rare sizes when working on bicycles, motorcycles, or automotive drain fittings, so the Titan bit sockets have worked fine so far.