I have written the product myself, and so of course I think it is the greatest thing since sliced bread. But you want to have a second opinion. Here's one (copied verbatim from the mail sent by commenter).
Having the ability to enforce constraints of arbitrary complexity by the RDBMS engine is priceless. Also, the two shortcuts for constraint specification (key and tuple) save a great deal of typing. Granted, this should be a part of any RDBMS engine but this was the first time I had an opportunity to try it and it's great.
Defining attributes independently of relations (relvars to be precise) is a great design enforcing mechanism. Not that any design should be enforced, it should be a major part of any IT project, but we all know how it goes. With this one and the separation of logical and physical specifications, one can build his/her own "columnar" DBMS (if such a thing exists) using nothing but a good "old" RDBMS engine.
There are two features I miss:
If I can offer a couple of advices to any new users of SIRA_PRISE it would be: