I went in November and you could eat at any restaurant. I think it is based on you eating the buffet dinner at your hotel but you can use it at other places. The voucher is for like 35-40 Euros each or something like that. If the meal costs more than that you pay the difference or if it is less you don't get the extra back. We had a couple meals at counter service places (A sandwich place on Main Street and the Pinocchio themed place in Fantasyland) and they used one credit for both of us. We did eat at the buffet at our hotel for dinner one night (the Santa Fe) and we had lunch at the MK one day at the Plaza Gardens.
The overview of where you can use the vouchers as in park vs. hotel is in the table.
And at the bottom it says the following: Further information about Disney Meal Plans
Whatever Meal Plan option you choose, lunch/dinner vouchers are accepted for their monetary value in all restaurants in the Disney Parks and Disney Hotels as well as certain Disney Village restaurants for a meal that includes a starter, main meal and a dessert or an all-you-can-eat buffet with a soft drink.
It depends on the hotel you choose (and the level of the meal plan). There are 3 levels, if you book the DLH you can only pick the highest level meal plan, but you can upgrade from the others. The lowest level only gives you buffets, the highest also the diner show and character meals.
My advise is to pick the restaurants you want to eat at and then do the math, for us it's never beneficiary to get the meal plan. (but that when breakfast was still included in the hotels (or we got a club level room), so the value got a bit better after that).