I wouldn't bother with the ground kit for the A99... it'll work OK as is and I wouldn't put much more money into it. 10m is kinda dead now, but when it opens up in the summer via Sporadic E, signals will be quite loud and your A99 up 40 feet will work fine.
The next antenna I'd actually put up for 10m is something like a horizontal *rotatable* dipole on a small, cheap antenna rotator or even a small beam.
A Moxon is a pretty easy antenna to make, and you can do it pretty cheaply:http://moxonantennaproject.com/
I used a simple ground plane antenna on 10m for a while... and something else too, maybe some longwire back in late 1995/early 1996 when I just got my Tech+. I worked some South American stations, a small handful of EU guys and a lot of guys around the U.S.
But eventually, I built a little two element yagi out of some aluminum my dad had lying around the barn and man, was than an eye opener. I put it up on 20 feet of Radio Shack mast with a Radio Shack rotator just as 10m was starting to open up a little more and I felt like king of the band with that thing.
But even a rotatable dipole will probably do better for weak DX stations than the A99.
It's good to have both, especially if your local friends are using verticals. For local communications, you need to match polarization with your friends, so if they're running a vertical, you need to as well. But for stuff that comes in via the ionosphere, you can use either a vertical or a horizontal but high horizontals tend to work a bit better in my experience.