Depends on the service. Some of them are really Safe, others are honeypot for NSA. Free VPN, are never safe. There is nothing such as Free. Where do you think they recover their cost of running servers, let alone profits? Never go for a free VPN. I would recommend ExpressVPN. One of the best, and has proven to have no logs (2017 Turkish Authority siezed a ExpressVPN server, they found nothing on the server, only data throughput) and they also run their servers on volatile memory.