Yeah, they're definitely harder to fill, and easier to overfill. What you wanna do the first time you use one is break the seal on the inside, replace the two pieces and just put drops in the little hole in the battery end, like 5 at a time, roll it around a bit, add 5 more, repeat until you get to 20-25 drops. Then on refills, depending on how far down u vaped the juice, the same process is used but only add 15 -20 drops. Important to let them sit after to distribute the juice throughout which will also help with less leaking.
My Boges leak too if I overfill with syringe or get some down the middle tube when dripping. There is still no perfect thing, unfortunately.