If you really liked StB and really want more then by all means dig in, though be warned that it isn't anywhere near the best that StB has to offer.
Animation:
The animation quality is pretty similar to the parent show, in other words pretty good. Expect all the main heroines to make appearances, even if they don't contribute meaningfully to the plot. There is a fair amount of action similar in nature to what we've already seen. The fights here aren't particularly long and involve the spamming of lots of shiny particles. There isn't actually any blood spilled in the OVA, instead they decided to focus on ecchi. Expect Kojou to lose his reservations towards ecchi acts and, for instance, show up buck naked to a bath with our other heroines who are of course topless. I still have a hard time believing that Yukina is supposedly 14...
Sound:
The OVA opens with a fast-paced but melodically weak OP and closes with a nice and calming song reminiscent of the parent show's ED- the singer's vibrato is pretty unique. The BGM borrows from the parent show and performs its role adequately.
The VAs all return from the parent show though I feel like Yoshimasa Hosoya had an off performance; he came across as a lot weaker than during the main show. Otherwise, you can expect solid work from Saori Oonishi, Risa Taneda, and Asami Seto. There are some new VAs in the form of La Folie's parents (including Mamiko Noto!) and new antagonists.
Story:
The story is a simple linear plot with good rising action and a decent overall progression. Given the length of the OVA, it's hard to say much in concrete terms without spoiling the fun. I will note that the climax is the kind of cliche that I've grown quite tired of and ended in an all too predictable way. Regardless, it was still a pretty entertaining watch; and given the early rising action, you'll probably want to finish the entire OVA in one sitting.
Character:
Despite the average-at-best plot, the character interactions are still fun; you still get Yukina desperately trying to hide her affections for our protagonist for one. In addition, you now get La Folia's family weighing in on her attachment to Kojou.
There are some blemishes here as well though. As is typical for these short pieces, there isn't much character growth. Likewise, you can expect pitiful, undeveloped antagonists. And of course, what I alluded to before, Kojou's character goes downhill here; let's just say he's not himself.
Value:
Overall, it isn't a bad OVA, I just happened to set my expectations way too high for it. It adds a mild arc that doesn't add to the parent story but is decently entertaining if a tad outlandish (in terms of climax and ecchi). The OVA is a fair, but nonetheless disappointing, addition to the StB franchise.
