gmax, from my chainsaw-using days I seem to recall that the total range of angles you operate the saw at, is fairly limited. I basically used them for vertical cuts or horizontal cuts, and the handles were designed so that the only way I could comfortably hold them for horizontal cuts had the fuel and oil tank caps facing upward. Of course the saws also got tilted a bit in the fore-and-aft direction. The advantage of the vents you have shown is that if necessary they can let some fuel out without doing any harm, and without interrupting the operation of the saw. However I'd be very surprised if the tank isn't designed so the vent is above fuel level when you lay the saw down, so whenever it isn't being used, it can let vapour out without ejecting liquid fuel. I'm not sure that line trimmers are always laid down in a consistent way when they aren't being used - mine isn't anyway. The bloop tube system guarantees that there will often be pressure in the tank when it isn't being used, so you are asking a lot of the bloop tube to hold that pressure indefinitely without leaking an occasional drop of fuel. In other words, I think the simple vent-line solution is better than a bloop tube for chainsaws, but I'm not so sure it's better for line trimmers.
