We used "keenserts" also in aviation overhaul/repair. I can't say how well they hold up over time as i don't recall seeing any used parts come in with keenserts that were damaged or pulling out. I liked to install them, easier than Timeserts to install, but as far as i know you can only use them in magnesium or aluminum parts. For steel parts i still think the best thread repair is a stainless steel Helicoil. Helicoils ARE fussy if you don't use a sharp tap ( dull taps are a helicoil nightmare ). Also when using any of these thread repairs usually a special thread tap is required, it will be called an "STI" tap. STI taps won't work for chasing out existing threads of common sizes... they are only good for making threads for inserts/helicoils.
Timeserts probably are the best but you have to have enough room around the diameter of the hole being repaired ( i would say minimum 1/8 inch ) so if you are repairing an 8mm threaded hole... you need to be able to fit at least a 12mm diameter area, more would be better. If you don't have room for that much diameter use what i am using. It's just a plain 1 piece insert that comes with a loctite type adhesive applied to it already. Or use a helicoil, but helicoils aren't my first option if the threads need to be oil or coolant tight.
Keep in mind these different type of thread repairs require special tools.
edit: EZ-LOK inserts don't require special tools, just the correct size cutting tap. I wanted to add a picture so you all could see them, but i can't figure out how to add a photo here.
About links for the mcmastercarr website.. can't do because it's a java program or something simlar.
EZ-LOK website is:
EZ-LOK