I had one regularly for years, as I had liver disease, then a compromised immune system. Am now fit and healthy, but had one this year because I have a baby at high risk of respiratory illness and, tbh, just couldn't cope with the idea of me having flu and looking after two sick kids under 4, one fairly high maintenance.
Years ago, dh had flu and high temps for a week which knocked him out, I did catch it but had a mild fever which lasted 3 days - so I guess it was effective. Never had flu the years I've had the vaccine, but could be coincidence, flu is actually quite rare!
dd2 had a flu jab aged 11 months, as she is at high risk etc, and had no reaction to it whatsoever. I've never had more than 24 hours of achiness/low fever in reaction, myself.
If you've had flu this year, you have some immunity for next year already, I think - someone medical told me it lasts a couple of years, in a non-specific kind of way.