If I sign up for a premium service from Roku, can I still view it from my computer or smartTV?
Is there any advantage or disadvantage to signing up for it from my computer rather than through Roku.
You can sign up for subscriptions for channels either through Roku or independent of Roku through the different apps, it makes really no difference. You use whatever login credentials to the apps that you used when you created accounts with those apps. As long as you use what login you used for the app, you can view them anywhere, unless the app has some particular restriction for location or number of devices you can stream. Think of a Roku device as kind of like a streaming cable box that allows you to get whatever channels you want to view.
Personally, I would ALWAYS subscribe through the service's WEB SITE. This way, 100% of your money goes to them (Roku/Amazon/Apple/Google probably take up to 30% or more of your fee), and you are guaranteed the best device compatibility. Plus, if there is any billing issue, you deal with them directly instead of going through a 3rd party. Also, when billed, it is obvious what it is for. When going through 3rd parties like Roku, the billing on your credit/debit card may not be obvious as to what it is for.
@andyross Andy makes a good point in regard to billing. In terms of access, you can view pretty much wherever the channel/apps allow.
Just to add: If you sign up through Roku, it will auto-log you in. Otherwise, you will need to sign in the first time you try to use a service (for some services, other Roku's on the same account will be auto-logged in once you do it on one Roku.) The drawback is that you cannot remove the app, and that can sometimes cause problems as some issues can be fixed by uninstalling/installing an app. Also, I'm not certain just how you log into the service on other devices. I'm guessing you might be able to use your Roku login/password, or does signing up let you set your own email/password?
Also, be aware that some services can be subscribed through The Roku Channel. I would STRONGLY advise NEVER doing that. Just like going through Amazon Prime, you can only access that service when going through The Roku Channel (or Prime Video in the Amazon example.)
In my experience, if you sign up via Roku, or probably any third party like Apple TV etc., you may find it difficult to use the service outside of that ecosystem. But, at least sometimes, you can figure it out.
For example, I originally signed up for Paramount+ via Roku. I couldn't use Paramount+ directly. In this case, they knew my email, but apparently, the Roku-created-for-me P+ account used a randomly generated password. (Which is good because it implies that my password at Roku is probably stored in a one-way-hash, or at least that they don't hand out my Roku password to third parties.)
But I wanted to use P+ outside Roku, so I canceled on Roku, waited for it to end, then went to P+ and did a reset password so I could enter a P+ password of my own and resume my subscription directly. So, I was able to do it, but it was a bit tricky.
Could I have reset my P+ password, gotten direct access, and still be paying through Roku? I don't know - didn't try. I was worried that Roku, paying my subscription, but no longer having the right password for the account at P+ might lead to trouble so I didn't try it.
Based on this experience, I think the simple answer is to sign up directly with content companies.
I guess my experience has been a little different with the Apps/channels I have used or subscribed to. I have been able to view channels/subscriptions on a variety of devices with no issues, other than jumping through the hoop of linking the service to how you are subscribed, like for example, ESPN+ to the service you use. Or in the case of Netflix, its restrictions on number of devices or regional restrictions. I am a bit surprised that the experience isn't consistent no matter how you sign up for a subscription. I will say though I have seen lots of complaints about signing up through a Roku subscription, but I don't personally have any experience with that as I have never signed up for subscriptions that way.
IN GENERAL - When you subscribe to (and pay for) a premium subscription through a third party like Roku, Amazon, Sling, etc., your account is with that third party, not the channel itself. In many (most? all?) cases you have to access this channel through that third party's platform. In Roku's case this normally means access from within The Roku Channel instead of the channel's own app.
If you'd like to use other platforms as well, your best bet is to subscribe directly with the channel on its own website. Then you can use the channel's website plus its app on any supported device including phones, tablets, and a range of streaming platforms, using the login parameters you establish with the channel.