Opera is a seriously good web browser. It is very pleasant to use and has a long record of exceptionally few security issues. The remark about the modest user base is accepted but the corollary of that is that Opera is rarely a target for exploits.
Opera Software ASA always responds promptly to those issues which very occasionally arise.
In all the nearly ten years that I have used Opera, I have never (yet) suffered a single security issue or incident with Opera.
Naturally, I expect to be 'tail end Charlie' with browser specific improvements from Avast but Agnitum Outpost Firewall Pro 7.5.1 works extremely well with Avast and so I now have Web Control as an additional layer of defence. I am not complacent but neither do I lose any sleep.