I'm not particularly bothered by this case (or more affiliate links), but when I see them in a blog post saying "This article / service is awesome, buy it", and there's an affiliate link involved, I do generally think "Yeah and how much are you making for saying that?"

But then I've done the same affiliate link stuff on occassion myself, especially when there's a perk link extra free space - it's easy to do, and as you say, not any harm as long as the intention isn't to mislead.