I've seen those. Never used one..... but I was taught how to use a grease gun at like 8 or 9. I don't have too much issue with them consistently leaking grease at the tip. If a zerk won't take, either the zerk is shot, the fitting on the gun is shot, or the part you are trying to grease is plugged. If you have a fitting that will take grease, but it leaks at the zerk, then the zerk needs replaced.
That said, I do have several types of ends on different guns. I have a long pencil style that I use to grease zerks that you can't get to, such as on a driveshaft where the regular gun fitting can't get into. I have another that is a right angle fitting, for those fittings that you can't get straight on to. And of coarse, a standard gun. I honestly have no desire to lock the gun onto every fitting, every time I grease. But, that's just me.
Just to reiterate, if you have a stubborn fitting that likes to leak.... replace the zerk. Works every time.
