It's a great deal for vans. Not so much for those with larger fuel tanks where getting enough fuel for a free shower is an issue. But for vans, all it takes is 20 gallons of fuel plus a $10 restaurant purchase (sit-down or fast food) within 24 hours, and you get a shower that stays on the card for 3 days.
If you drive a diesel van, make sure to swipe the card both at the pump and at the restaurant, and the shower will automatically be on the card. If you drive a gasser, you can't swipe the card at the pump, so you'll have to have the receipt on hand, as well as have the card swiped when getting a meal, then present the card and the gas receipt to get the shower.
I recently got fuel while under a load and the next day had lunch at another TA. Both the fuel and the food purchase happened within 24 hours, so I got a free shower loaded onto the card. Two days later I took the shower. The fuel I was gonna get anyway, and the food I was gonna get anyway. The free shower was a free bonus. At times when I know I probably won't be eating at a TA to get the free shower, I'll often fuel at a Flying J, despite the discounts at the TA, since a lot of the discounts at the TA don't equal the free $10 shower at the J. The discount at the TA needs to be 25 cents or more, over 40 gallons, to equal a free shower at the J. Actually, with the $1.50 transaction fee for the Comdata usage, which adds $3 to two fillups, the discount needs to be 32.5 cents at the TA, otherwise filling up at regular price and getting a free shower at the J is a better deal, especially now that all you need is two 15 gallon fuel purchases at the J to get a free shower. But at times when needing a shower isn't an issue, the TA is always a better deal. Again, this is for vans more than trucks.