It's always fun finding merchandise for Batman Forever that I've never seen before. After several years of doing this website I thought I knew pretty much everything that was made for the movie. Trust me, I own an awful lot of it now.
Anyway, it's a neat idea. Selling a t-shirt in a novelty case. That way you get a bonus thing to play with while you're wearing the shirt (which is great for kids). You could almost use it in place of the Kenner Batmobile - just think of how many figures you could fit in it - at least 7-8.
As mentioned in the video I have no idea why they chose to use the Jean Paul Valley bat symbol on the wheels. That's going to have to remain a mystery for now.