not starting an argument here, but IF CRIMPED CORRECTLY They are perfectly fine. yes i agree the fools that use side cutters to crimp and wonder why they fall off are ridiculous , but they are honestly fine. I ran some on my last bike on my coil connections & they we fitted on the bike for 15 years with no problems at all. the rubber boots you mention are a good idea if the connectors are exposed to the elements as they help stop corrosion of the connectors and prevent accidental shorts.
Best practice for fitting crimp connectors is always to use the correct size for the gauge of wire you are using them on, if you can : Tin the end of the wire with solder to prevent future wire corrosion (old blackened copper = bad) use the correct crimp tool and fit a protective boot where possible.
There is really nothing bad about crimp connectors, just the people that use them wrong.
if the tack wire breaks or "fall out" due to not being fitted correctly , it is really no big deal, you WONT get stranded because of it. i would rather advise to use a crimp end piggy-back then a inline wire tap. Wire taps are bad on so many levels (damaging & weakening original wiring for starters). and definitely do not advise twist and tape crap either