I've had Grindr on my Ipod Touch for a year now, it's not that new
As always, safety should be your first concern. If the guy is strange, I'd block him. If he's a good conversationalist, then why not ask him out for a coffee. Good gay friends are harder to come by than good straight friends; partners are even more harder.
There are malicious people out there, but if they are actively hunting gay guys on any social site or even here on GA, they will eventually find someone. If it is that 1 in thousand intimidation factor scaring you from making mobile friends and connections with others, remember fear is best weapon anyone can ever have against you. Whether by action or inaction, don't fear the outcome and live as you would.
On a side note, Manhunt is the worst of the websites mentioned for gay guys based on personal experience, long story about a 50 year old guy during my first year after I began exploring . Craigslist has a bad reputation, which 90% of it is deserved, but 10% are actually people looking for friends and good relationships. I've met a few friends from Craigslist, so I'm not that anti-Craigslist.