I have OP5, after two years with OP2. I think it's a solid phone with some wonderful performance, solid battery life and great responsiveness. I'm glad I bought it, even though there are things I would like changed or simply different.
While it's absolutely top of the line now, OP does have pretty awful history with their ROM. It's great, but they seem to forget about their older hardware just as soon as the new flagship releases. Having that said, ROM scene for OP phones is very much alive and with just a bit smarts you can have the newest Android for the long time, if that's your thing.