Mints actually do their main reproduction via runners, many don't set viable seed. I've seen mints grown together in many an herb garden with little problem other than the strongest grower will overcome the weaker.
I have no idea of the *mechanism* (honestly I hadn't even thought of crosspollination and reseeding, although in principle I suppose it's possible)... all I know is when I've grown different mints right up against each other they never seem to taste as good <shrug>
I know of beekeepers who keep bees near field of mint that have mint flavored honey - not necessarily something I'd like together, but some may like that taste.
I made the mistake of going by memory instead of re-checking. As normal, everyone is right, at least partially or in some way. I've looked at several sites to try avoid the problem of believing everything I see on the internet. There is not always universal agreement, but what I think I learned is
Mint does propogate by runners. It also propogates by seed. Mint propogated by runner will remain true. Seeds, however, are another thing. Mint is pollinated by bees. Some bees can travel a long way and cross-pollination can alter the flavor. Someone suggested that self-pollinated mint could also have altered flavor. Recessive genes, I guess, but I'm a little sceptical of that. Maybe they only thought it was self-pollinated.
Several sites suggested removing the flowers so it cannot reseed to maintain flavor. One suggested that propogation by runner is so intense that it will limit the starts from seed, thus somewhat preserving the flavor, at least until the stand of mint weakens.
The conclusion I think I've reached from this is that if you do not let it flower and set seeds and rely only on runners, it will remain true, even in close proximity to others.
The banana mint I have sniffed at Richters' (link in the post before yours - they happen to be about 10 minutes from my house, neener neener) honestly does not smell at all banana-y to me, and is not among my more favorite of their mints -- but everyone's nose is certainly different.
My sister gave me several mints from them for my birthday last month, and my outstanding favorite is their 'Swiss Mint'. I am not in general a peppermint person, but this (which is not *completely* peppermint-y, although there is a strong element of that) just smells soooooo goooooood. I've planted it in a bed that I pass and weed a lot, just so I can sniff it in the process
Oh Pat you are Sooooo Lucky to live close to Richters I plan to purchase from them for my Herbal tea garden. Of course will include severial mints.. :watering
I bet their place is amazing :coolsun