You might gather information from references the vendor gives you, but such contacts tend to be canned. Of course, a search of the Internet can be useful. Another option is to hire a consultant, preferably one who knows the legal industry. But don't think hiring a consultant justifies abdicating your responsibility to evaluate and decide. Consultants generally know a lot about automation, but they do not know you the way you know yourself.
Consultants also tend to be conservative in making recommendations.
They don't want to be wrong, and there is always some uncertainty about how much risk you are willing to take and whether you have the know-how to assimilate and operate the technology you are purchasing. This conservatism is not necessarily bad, but be aware of it. Even if you determine that the program is worthwhile, there is another factor to consider before purchase. There is only so much technology a firm can absorb. Make sure your hardware is strong.