is the content similar across providers??
I've never honestly seen the content overlap between providers, so much like how the world of streaming video has segmented off into individual corporate providers much how like cable TV did, legit manga sites basically offer you titles that each company owns and you'd need to subscribe to multiple sites to get everything being offered.
If you're interested in the SJ titles Viz does though, you only need an account to stay current. I believe the first 3 chapters and the most recent 3 chapters are available with free accounts, you only need a paid subscription if you want to access chapters outside of that.