Users spend 80% of their time looking at information above a page fold (see "Scrolling and Attention"). But somehow they need to pick the right product. So instead of thinking of this pattern as generally "good" or "bad" ask instead, "How can I get the customer to pick the right product the fastest?"
A pattern based on questions
If you were in a brick and mortar store and they wanted to purchase a mat, you could start out by asking "what size area do you need to heat?" In the UI this could translate to a dropdown list with the different sizes. After that they would need to pick the wattage. And so on. This pattern is called "Cascading Lists". This helps eliminate the noise of products for which they're not interested.
A pattern based on browsing
However, customers might want to browse and see what they can get based on the price instead of specifying a heating area. Another pattern is "Active Filtering". This pattern supplements the list you provide while minimizing how often users should spend scrolling.
To answer your question, this could be confusing but not a deal breaker. I think the more important issue is figuring out a pattern to get them to the right item without relying on them to scroll and find it in a list.