Should I go through the interview process for "training" purposes?

I have connections at a massive brand name saas company, let's call them Company A, and i know my end goal is to get an AE position there. My contact said in the new year they will almost definitely have roles open for my experience level/region etc.

Was reached out by a recruiter from a well known saas company, let's call them Company B, their name is regularly discussed in their industry, etc. Usually don't speak to recruiters often but this one caught my eye so I decided hey why not, let's see what's up, see what kind of questions a bigger player would ask. The role is for a mid market AE position. For reference Company A is 10x bigger than B.

Anyway, I spoke with the recruiter, a day later they email me saying they want to move me into the 2nd round and speak with the hiring manager next week.

If my end goal is Company A, should I still speak to Company B and string them along? Is it worth the "training" or experience of interviewing, or am I just wasting everyone's time? Should I still go through the motion and potentially get an offer so I have a better grip of my market value?

Thanks all!