That's why I don't buy bumper packs of biscuits!
It looks tempting to me. If you have the money it's worth giving it a go. People spend on occasional treats such as hay-cubes or carrot cottages so why not fresh grass? They will mow it down within hours but that's what it's there for! Established grass grows pretty quick so if you have the space to put it elsewhere (outside on a balcony or near a window for a week or on a table outside the backdoor) and give it a bit of water it should grow back. Personally don't know if I'd bother with the metal tray bit as piggies also love to chew cardboard!
But If I was hoping to move my 'patch' and re-grow it using a tray might be easier.
You can get rolls of turf from garden centres or B&Q for about £5 each but these have usually been rolled up for a while so would have to be unrolled, put somewhere suitable, watered and left for a week or so to recover. These would not be available in winter, but if piddle patch comes all year round that'd be cool.
I have a stone planting trough with 3 lavenders in and I used to tip the dust from the bottom of the hay bag into this. Now you can't see the lavender for hay grass and I've got to root the whole thing out and re-do it, which is a bit of a nightmare but I'm going to let the pigs help

If you have a big plant pot with some soil in it's worth a go - the grass that grows from the dust in the bag should be super appealing. Good luck, and what a kind owner you are x