It is a single-use tool: it tests mobile usability of a website or code snippet. This is useful before, during, and after the development process. So, if you are developing a website, then the mobile-friendliness tool is a necessity. Its also useful (in conjunction with Page Speed Insights and Search Console) in developing a full idea of site performance and how it relates to SEO.
SE Ranking is on a good track when it comes to rank tracking. It displays a graph of your average position over time which is helpful and it can also help you when it comes to identifying some basic SEO issues with your website. It boasts as an all-around SEO tool, which it definitely isn't because it lacks a link database to be your go-to tool for everything SEO. Its UI is not optimized for ease of use, thus offering sub-par user experience. It has two different interfaces for different SEO tools which, I hope, they can incorporate into one.
Google does not cross-check the results from other search engines in the creation of the tool. Bing and Yahoo might not consider your website mobile-friendly, even if Google does.
Some devices and screen resolutions were not thought of when Google created the tool.
The output of the tool is not specific enough, at times, for web developers.
The support is great but they don't have 24/7 support. And time zones can also be an issue sometimes. On the other hand there are plenty of guides and videos around to get yourself started. I never really needed support for "big" issues. And the help I got was good enough.
The Google Mobile-Friendly Test is much better than Bing Webmaster Tools to ensure our clients' websites are mobile friendly responsive. Google's tool is created specifically for most of the online searches from the internet, and most modern devices, modern browsers, and screen resolution settings. Bing is not as technically advanced as Google and not as specific in their tools, to ensure the creation of mobile-friendly responsive devices.
SE Ranking was our choice based on the suite of features it offered compared to competitors as well as the # of projects you could manage. From a cost perspective, we feel it provides the most value for your money. Other SEO tools did not offer the lead generation features that SE Ranking offered as part of their monthly plan.
The website "health" report has allowed us to fix things that Google might find strange or cause us to lose rankings, which has been very helpful.
It's given us more visibility into what exactly our SEO management company is doing and how they are performing, and if things are changing or not. It's very easy to see right from the dashboard.
Being able to see how our competitors stack up against us has helped us know where to improve, what to focus on, and how to be even better.