If you notice your site is taking a long time to load, then you should first use PageSpeed Insights to see what can quickly be optimized (also check your file sizes, hosting server, NGINX and other common sources of slow speed, too.) And, if you've notice gradually fewer Organic Search visits, PageSpeed Insights might be able to help. As Google is reducing the prevalence of slow sites, you could be losing traffic. Speed up your page load times by finding what is blocking renders, slowing down contentful paints, and other critical page speed signals.
SE Ranking is a fantastic tool if you are a marketing agency or freelancer looking for a single tool for the majority of your SEO work. It also includes B2B tools like their lead generation widget and white label reports that can help you generate new leads for your business. It would get 10 stars if their database was larger to accommodate research for small geographic areas, but they are always expanding their database so it may just be a matter of time. Research SE Ranking has pricing plans available for every budget.
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.
I think GTmetrix has some feedback that PageSpeed doesn't provide, but Google's tool is easier overall and has a better user experience; also offers compressed images, CSS, and javascript files if that's the case. Also, Google has extensive documentation to help you better understand what can be done to improve your grade.
SE Ranking is better than Serpstat or MOZ or Ahrefs when it comes to tracking keyword rankings, but it lacks in every other SEO category, such as onsite and offsite SEO metrics, content analysis, etc... It's a good choice for agencies that are interested in tracking keywords for their clients, but other than that it underperforms in every other SEO category.
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.