Hi, sure, I use it every year, it works perfectly for me. It requires a bit of practice but it's the easiest solution to deal with varroa for me. I use the same approach to apply oxalic acid.
At my place, when we smoke meat, for example, we use that kind of string to tie everything together. Something like this: smokehouse.guru/en/products/string-for-tying-meat-for-smoking-55.html. The main thing is that the string needs to be able to soak out the acid from the bottle.
