I should add that there are a lot of free channels available with a Roku. You can add them and drop them at will. For example, my husband found a couple of free channels on cooking that he likes. I like Newsy, a free channel that offers a quick recap of all the major national news; Newson, which offers a replay of a local news channel; and I sometimes watch the major news channels such as NBC, CBS which offer snips of their own broadcasts. All of these free channels that I have mentioned (with the possible exception of the cooking channels) have commercials, but they are easier to watch than standard commercials because they are shorter, most 30 seconds or less and are not as frequent.
The subscription channels we have -- Acorn, Great Courses, Netflix -- are all commercial-free, which makes it much more enjoyable to watch a tv series episode. Amazon is also commercial-free, whether you are watching free Prime shows or paying to watch one of their non-free offerings. (I am never willing to pay, but my daughter sometimes pays for a movie or tv series year that she really wants. These are all pay-to-watch for a specific period of time.)
The biggest problem we have with Roku is finding specific things. Having a search feature helps a lot. Our Roku 3 has a voice search which is very useful when it works. Having to type in a search can be a pain. There is so much content on streaming channels that it really helps to have a Roku with a useable type of search option on it. For example, I can do a voice search on "Maigret" and Roku will come up with a list of clickable links to everything that has Maigret in it. Without a search option, you can spend a lot of time fruitlessly looking for a tv series you want to continue watching but can't remember which channel it was on.
As I mentioned, I think all of the subscription channels have a free trial option. You typically have to put in a credit card to start the free trial, but you have the option of cancelling it before your card starts being automatically charged. You can also add channels via Roku.com which can be convenient. That website will give you some basic information about the channel, but it's a good idea to also Google the channel to find out what customers say about it. That is how I learned to steer clear of Sling. Sling may get better down the road, but it has too many complaints for me to even want to try a free trial on it (because there have been complaints about difficulty dropping it). That is the only subscription channel I have been interested in that had a lot of complaints, though. Acorn, Netflix and Amazon all get good customer feedback.