I like watching fishing stuff on youtube and actually found my way here from Glenn's channel. I've also plenty of videos on other channels like the rod bending videos that Omnia does to be informative and while I don't always agree with everything Tactical Bassin says or promotes as the best rod for <fill in the blank> they have posted a good amount of stuff on their channel that I've found useful. Even some channels that seem silly have tought me something at some point or have at least been entertaining. I've checked out a few of THEREELTEST's video and agree the whole channel does kind of seem like one big Shimano commercial. I also personally don't click the videos to get a bible quote thrown at me right away, but I have found a couple of them useful since they do go over specs and such. That said if I am looking for that sort of thing (Shimano specs) I'd probably start with JP DeRose's channel. He clearly points out he's sponsored by Shimano (and the other brands he works with) on his site and IMHO his channel is a little more professional in terms of going over the features / benefits of those products without trying to make it seem like he's just some impartial fisherman and just promoting one of them because it's the best (or saying negative things about competitors).
Also, in terms of using youtube videos to make gear decisions I'd take anything on there with a grain of salt (or several if the creator clearly has some sort of relationship with the manufacturer). Truth be told there are a ton of people getting paid to 'shill' and youtube is just one of many ways they can do that. I'm also not personally against doing that as long as you aren't trying to hide the fact that you are getting paid to promote a certain product / brand. If I'm considering something new I generally look for as much content as I can find about online whether it be here, youtube, or review articles. Then if I do decide to try it out I've found it's best to just try out one rather than going all in and ending up with a bunch of stuff that you thought would be awesome but ended up not turning out to be that great.