I try to base all my groups are dynamic queries, but I can see the need for this if you are adding nodes/interfaces to a group manually.
I think you are right, dynamic queries are best but this customer has loads of groups. Would be good if you could copy dynamic queries between groups.
For me, I would want this page to include something similar to the NCM "Config Management" page. I would want to be able to take/run action(s) on the selected nodes. Perhaps download the configs, or run scripts, add them to a group, bulk edit, add license for X product. I do not like having to go to a completely different page, which is basically the exact same page, to run product specific commands. I don't mind keeping those pages, but I would definitely want to include the basics from each, at the very least. Hopefully these things will eventually appear on the manage entities page, if they ever get that thing up and going.