I use Reka Rail checks and Reka checks all the time. I buy Reka Rail checks at Manor at a discount on their face value (currently on special for 4% off the face value, normally 3% off) using the store card.
I use them for public transportation purchases (GAs, monthly passes, individual trips) and haven't had any problem using them instead of Swiss francs at SBB desks. They generally give change above 10 francs in Reka checks and under 10 francs in Swiss francs. The ticket machines won't usually return more than 20 francs in change when you use Reka to pay, so I recommend getting the 10-franc Reka checks rather than the 50-franc checks if you make smaller purchases.
If you buy a 3,860-franc GA, you save 115.8 francs by buying Reka Rail checks at Manor with the standard 3% discount and then using them to pay for the GA. Since my wife and I both used GAs, we saved around 200 francs. All in all a good deal if you spend on SBB or other public transportation.
The Reka checks (not Reka Rail) can be used at some gas stations, hotels and ski-lifts as well. I believe Coop sells regular Reka checks at a discount to its store card users. I just use the Reka checks I get as change for Reka Rail at SBB desks.