Specs:

This Diamond is sold as a solution for mobile use like cars, and is supposed to work without counterpoise.
I can easily open the local repeater on 70cm at about 50km with the 5 watts my handset delivers, so big hopes for this one ;)

This looks promising on the 2M bands, let's look at the 70cm:

Owkay? This antenna is pretty well tuned, as it is sitting in my window sill… Let's focus on the HAM bands:

SWR at the 2M HAM band is pretty flat and well below 1:1.5 so that's good! How about the 70cm?

It's even better! This confirms my thoughts of this stick: A solid performer, albeit with a 2.15dB on 144MHz and 5.2dB on 430MHz. If this stick was on the roof it'd perform even better, and be pretty stealth while doing so ;)