$.02
take the interview. if they are serious, that offer is your bargaining chip with your current shop.
you can go to current dude, and go look man I'm getting 25% (whatever amt it is) raise just by leaving here, will you match/make better counter offer? sweeten me up bro.
if he says go fck off - OK no worries here is my 2wk notice, thanks for your employment.
if he says 'damn nick, you are our best mechanic, here is 10k raise' - then you have a decision to make.
I have no idea which job fits you better long term.
myself - a guy that has had 2 different careers (machine operator, and now I.T. guy), and never had 1 job longer than 5 years, in either career - I totally 10000% believe in moving around, and taking the risk. for sure in the technical world, thats pretty much how you move up/grow. its rare, at least here in TX, to be promoted at the same company enough to outweigh a job change. what I mean is, I can get a 3% cost of living raise if I stay another year, or I can get 10% raise by switching jobs.
if you got skills and you know it and are sure of it and good at it, a job will find you.
again - if its a real offer - I would go for it, and lose 0 sleep over it.
- saylor