Flora and Parsnip have astro-turf covering the concrete slabs in their kennel/run. Fortunately for me, they never chew anything so I'm fairly confident they won't touch it (they've not to date anyway). I found that they were slipping on the slabs as they aged and lost muscle tone and needed something that they could easily grip when they hopped around. But it had to be something weatherproof as the run is open to the elements on one side (it's a bespoke kennel and run). I was lucky and found an offcut in B&Q - it's the really short stuff that you tend to find in greengrocer stores. I paid £20 for it and it's around 5 ft by 15ft.
ETA - I wouldn't get the 'posh' artifical grass because it's too long and would be way too tempting for a bunny to nibble. But I think you're OK with the really short stuff, as long as your bunnies are not chewers.