I flocked a box of these a few years ago.
I just went with PVA glue and the Kallistra flocks. The main colour was the darker Marsh Green, with the lighter Spring Meadow for variety. I didn't texture or pre-paint the plastic.
I washed the tiles before starting and used full strength PVA. Despite that, the tiles were slightly hydrophobic in places. I sealed them after flocking with watered down PVA sprayed through one of those travel mister bottles.
It looks okay - not as good as the originals - but worked well enough. If I was to buy any more, however, I'd get the pre-flocked tiles. Having used the Kallistra flocks I shouldn't have any colour matching problems
There are a couple of regrets
1. PVA doesn't really have a smell, but if you have a dining room table covered in it, you start to notice it
2. Having spent a couple of weekends with the dining room table and couch covered in tiles I was given a 6'x4' mat about a month later for Christmas
I've never used them for a game. The one thing that worried me was clipping the tiles together, but I don't know if that was justified or not.
If you can find it, "Making Terrain and Buildings for Historical Wargames" by Timothy Hall and Jonathan Sutherland has quite a few pages about the terrain, including building custom bits.