The Stans injector is probably one of the most overpriced but still useful TL things I've bought. Much easier and cleaner than just tipping sealant in and out of tyres.
Someone gave me a syringe thing that I thought I'd never use but actually came in useful when using Stans race which just blocked up a small Stans bottle.
I bought it years ago for my first tubeless setup. I also wasn't using Stans sealant so that's no use and it has proven to be very useful over the years for doing tyre swaps and stuff, where you can suck out sealant and reinject not make such a mess as the tippy tippy squirty crew.
The Stans injector is probably one of the most overpriced but still useful TL things I've bought. Much easier and cleaner than just tipping sealant in and out of tyres.