The intial all-over application was hard to work in and rinse out, mainly because I used honey in my mix, I think. However, you usually only do that once or twice a year. Root touch-ups are much easier all the way around, and they're very forgiving as far as overlapping old over new, etc. I just co-wash it out with conditioner, and it only takes at most two conditioner applications to get it all.
Now I've switched to a henna/indigo gloss to blend in my greys, and I don't even have to wait for dye-release with it. It only uses a tablespoon or so each in a conditioner base, so it's very easy to apply with a color applicator bottle and rinses right out. I just apply it all over every other week or so - whenever I start seeing any little glint of silver at the roots. I have fairly dark hair, so this works for me. It wouldn't necessarily for lighter colored hair or for anyone wanting an all-over red shade. The latter would require full dye release.
Anyway, I'd be wary of any henna product that isn't just plain old henna. When you aren't, you're apt to get something that contains metals, compounds, or salts, and that's
what can react badly if you go back to regular hair color.