I did gnail, with Giotikas too as it happens. Don't regret it, glad I chose it over precise.
You'll find in Athens the majority (around an 80/20 split) are using gnail. The precise users tend to be Americans who are extremely concerned about muh FDA approval.
1+2) I wouldn't however really say one was better than the other and the majority of people got the results they wanted no matter the nail they were using. Precise makes going to physio harder work as you will need to use your wheelchair and walker to get in the taxi, whereas gnail patients can ditch the wheelchair very early on and eventually just use crutches. You won't be having a massive social life whatever the nail used, I didn't really see many gnail patients going sightseeeing or socialising and neither did I - in theory in might be possible but in reality I (and seemingly everyone else) was just too tired to do it, and 'full weight bearing' doesn't mean you won't get drained of your energy quickly when out walking. All I saw anyone manage was going to a restaurant for lunch, and even that was rare, most people were strictly staying home and ordering food in and only really went out when it was time to go to physio.
3) Yes flying home would certainly be easier with the weight bearing nail, although it's not like Precise patients couldn't fly home either. You just have to arrange an airport transfer with a taxi who will carry your bags for you, get a trolley at the airport etc - it's doable. Gnail patients were up and walking quicker and back to 'normal life' faster, that's true.
4) It can be difficult and painful at the start, almost everyone finds it gets easier with time. For some people it's easy right from day 1. I never met any patient in Athens who had to stop lengthening early because of this, although for sure at the start it's challenging and time consuming whereas Precise is easy.
5) Nail bending (not breaking) was a significant issue, but it wasn't limited to Precise or Gnail alone. There was a not insignificant minority of people who bent their nails, so you have to be careful no matter what you choose (and even then it's possible just to be unlucky).