Yeah, I know. Life sometimes calls for compromise. The plan is not to mount my 10m antenna w a mag mount, but with a hood seam mount in the trunk. You may remember that you told me not to use that type of mount, but then recommended it to someone else in a different post a while back.
I'm looking at several antennas right now and am leaning towards a larsen nmo27. I asked about this one because googleing was not turning up much and I was curious.
The question was has anyone actually used one. I'm guessing your answer to that is no.
Any mobile antenna, less than a quarter wave in length, will have additional loss. How much loss depends on the Q of the coil, the overall length, and on the mounting methodology; in that order. In this case, the coil Q is very low, the length is compromised, and so is the mounting; a mag mount in this case.
The question remains, will you be able to make some contacts? The answer is yes, but the rest of the folks running full-length 1/4 waves, will work stations you won't be able to, unless the band is in very good condition. At present, 10 meters is very sporadic. You need the best you can do, and that certainly isn't a mini-hamstick, stuck on with a mag mount.
There is a lot more about this subject, on my web site.