Why does my meta tag checker show & instead of &?

Your title is fine. In HTML source an ampersand is written as & (the correct way to encode it). Browsers and Google decode it back to & when they display it.

The checker is showing the raw encoded form instead of decoding it first. It should decode the value, then display it safely as text.

Good to know. Does the same encoding affect how long the checker thinks my title is?

It can. If a tool measures the raw source, "&" counts as 5 characters instead of 1, so your title is reported as longer than it is. Title length should be measured on the decoded text, and ideally in pixel width, which is what Google actually cuts by. We fixed both of these in our own checkers after spotting the same thing.