I have the Lezyne Road Drive, and I like it a lot. If you can comfortably carry the large size that you mention, the extra volume is nice.

When I install a new tube, or add it to the pack I carry on the bike, I check to see that the valve core is tight.

When I use the pump, I don't screw the head onto the valve stem super-tightly (not necessary), and I use the bleed valve to relieve the pressure in the line before removing the head from the valve stem.

So far, I have had no problems with accidentally unscrewing valve cores.