This is my second season of cutting Honeysuckle on DNR land. As such, I use 25% Glyphosate, which is aquatic rated "Farm General" brand from Home Depot. It comes by the gallon at 53% concentration, and I cut it with an equal amount of distilled water [25% concentration]. Don't use a chainsaw since it requires certification and bio-degradeable bar oil near wetlands. I have cut n painted Hive Queen Honeysuckle, at least 4" trunks, and it did not resprout. Spent New Year's Day 2020 sitting in the snow and cutting Honeysuckle. Saw a earthworm above ground, surrounded by snow [south of Sugar River]. This season, I've been cutting over by Whitewater, some by Avon, and for Honeysuckle, applying a ring of 25% Glyphosate to the cambrium kills them daid. But I always cut n paint in non-freezing temps, roughly September - March. Unfortunately, they start leafing out in late March, so I stop cutting.
Switched from a Silky Saw "Big Boy" XL 2000 when I kept running into fencerows of HS, now I have a 20v reciprocating saw. 20 oz of 25% mix does me for four hours, cutting alone. Use distilled water for a mix, Glyphosate really loves to bond with calcium, manganese, iron, and aluminum [IIRC].
I have a Buckthorn Blaster here, never used it. The idea of trying to remove the felt button and refill the bottle strikes me as something I'd rather not do. Got a Birchmeier sprayer, and it has a wide mouth for refills, does not leak, and has a flexible weighted pickup head that allows use in darned near any orientation. I started with a hand sprayer from a local hardware store, it leaked around the finger trigger and the bottle could rotate off the head and fall off after using it at different angles...
I started to cut Buckthorn this season, so I can't be sure how effective the 25% Glyphosate will be, but the DNR biologists recommend it. Except on Black Locust.