Hello,
It's not really about the theme you choose, it is more about the developers that make it.
If you are going to rely on a third-party developer, you really need to research their prior history as you want a team that has a good track record in all departments.
From their deployment of there theme's, amount of Updates they push over time, Community Support, and their Customer Engagement. You also want a developer who has a track record all their previous theme they released with their continued support and regular updates/tweaks.
Depending on your theme, you will also face a degrade in the speed of your shop. This is due to the junk that comes along with the themes.
I first started off with just the Standard StoreFront Theme, along with a handful of purchased plugins/add-ons. - It is a very clean barebones theme, which made it very fast and very Secure with no hacking attempts ever got through.
I have no moved onto the Flatsome Theme on ThemeForest. - So far it has been ok, however, there is a massive degrade in my website load times. I haven't launched yet so I can not really confirm how secure the website will be, with all the junk it requires. I am also looking at increasing my sites security as well for this reason.
