It might not *technically* be flirting, but if I see a beautiful woman who takes my eye, I have no qualms about telling her she looks fantastic. Rarely is it with any intent, but in 95% of cases they just grin and walk away with a face-wide smile, in 4% of occasions, I may get a glare or even a slap, but in 1% of cases, evenings take a turn for the better.
It's worth it for the smiles, let alone the occasional unexpected 'liaison'.
Seems a reasonable thing to do. On the rare occasions people tell me I'm looking good (blind people, retards and job applicants mostly) it does lift my spirits and make the day fly by.
Honesty is always worth the risk.