We had short debate about this in planning for SQLSaturday #21 – Orlando. One of the sponsors wanted to have some time to do a demo of one of their products, beyond a table at the event. IMO, there is nothing wrong with an event providing that time, provided it is made clear that this is a vendor sponsored session and will be a bit a of a sales pitch.
I know I would appreciate articles/sessions on a specific product. Comparisons articles are great, but you can’t really be an expert on each of the products, so I’d just assume learn about why you chose the one you are using, how you are using it, and what are your favorite and least favorite features.
I’d personally accept a session to an event that was something like, How [Insert Product Here] helped me do X, provided it was submitted by someone not employed by the vendor.