Did you test v6 before?
No
May I suggest that you test before going to production? v6 is so much different from v5 that it's not just simple upgrade.
I have no test environment and this is relativelly small client, there are only 40 eset clients and I have no politics or some jobs on ERA. I use it about 8 months (version 5). It could be possible to deinstall version 5 without any backup and install the version 6, but I want to try the migration process on this small client.
It does not matter if you have 5 or 50 clients. The philosophy of v6 is so much different that you might stumble on large number of problems.
If you don't have complex policy in v5 you might be better with clean install. But even then, you will encounter many problems.
You should setup virtual environment and try testing, and then decide. You won't regret time spent on test.
O.k., I try it. I have many clients on version 5 and they will need upgrade in a future