I started out with Roku several years ago long before DP existed. Never was able to get my channels published and really just used the demo brightscript and added my content to it. As far as the others, they didn't come close to making developing easy.. When Roku released the DP, it made it even easier, at least for people with limited amount of content. I am just now publishing my fourth public DP channel. Simply because not much fits in the DP, and I can not for thel ife of me get the "series" format to work, so each vintage tv series becomes it's own channel.. LOL
I have about 4-6 more channels to publish but am spacing out the publishing as to get them into the spotlight over time as opposed to all at once. Kinda like free advertising..
Anyway, I have tried to develop for kodi, amazon fire and several other generic android based boxes. But with the amount of learning another coding language and another set of poorly explained directions the fact that Roku has a much larger audience then any of them others I have just stuck here with Roku.
As a user I love my Rokus, I have one in the bedroom, one in my office and a roku tv in my livingroom. I also own a fire tv and one of those dangles from google.. I used them a couple times and use my Roku all the time... About 4-5 years now it's been roku even more so then the cable boxes...
Of course I am not a HD infatuated person, I love vintage SD TV, and most of my original productions are still in SD. It doesn't seem to effect my audience at all, we have over 1 million active users between Roku and the web site, 2750+ videos and we run the servers ourselves, server 2012 r2 (just upgraded last week from server 2008 r2... I've been streaming video through the web since 1992, of course back then only a few users had enough bandwidth to watch our stuff, lol. And before 1992 we ran a very popular BBS that was almost purchased by AOL, but I didn't like the price they offered and really enjoyed being a SYSOP...