I want to be able to see my library's data in Apollo as if it were migrated, without affecting my current ILS. There's just no other way to be confident that it will be transferred correctly and completely.
Yes, indeed. You can try Apollo free, with your data, and with no obligation. All while your library operates normally. It's exactly as if you migrated. So surprises on migration day are virtually eliminated. Your comfort and confidence are paramount, so take as long as you like and feel free to ask questions.