We have not tested search analytics (mainly because its a niche of a niche), so I can't comment on their performance.
As a general point, you should consider how deeply those search analytics work with a particular VMS. For instance, 3VR is optimized for search (how much, one can debate) but 3VR would work poorly with Genetec because it's completely separate.
I am assuming you'll want maximize integration between the VMS and search analytics or else it will be a real usability problem. So, to start, I'd check with your VMS (Genetec, etc.) and see what and how much they integrate with.
Btw, from what I know of Ipsotek and their website, Ipsotek positions itself as much more a traditional alerting / scenario based analytic while Briefcam is much more of a search solution (no alerting).
Agent Vi has an analytics based video search product.
The product is integrated with Genetec VMS and supports searching through a very large number of cameras. You can search for people, vehicles and objects.
You can find further details in Agent Vi web site.