I have just back from a last minute weekend trip to Belgium. I spent all of last week trying to find the best deal possible to over to the continent and this was by far the best. As long as you return by midnight the day after you leave, you can get any train you want.
We left early on Saturday morning and came back late last night to get the most out of it. The cheapest ferry I could find to go over the same period was £90, so it in my opinion it's a great saving. OK, so you have to leave early in the morning, but if you are only going for two days it is worth it so that you can spend as much time as possible over there.