Simple Newbie Question

[Kata Pa]

When we run the PageSpeed insights, we are given quite a long list of recommendations (even though Mobile page speed comes up as fast, optimisation is medium).

We are a bit confused about the PageSpeed Modules option (https://developers.google.com/speed/pagespeed/module/)  ... is this literally something we can ask our developer to install on our 1&1 Apache server and all the recommendations will be automatically done?? Sounds too good to be true!?

Also if installing PageSpeed Modules can fix it all, why is there Lighthouse (https://developers.google.com/web/tools/lighthouse/) which apparently allows developers to go through each URL one by one to find all the areas which can be optimised?

In summary, our question is what is the most efficient way to ask our developer to improve PageSpeed optimisation (if this is something he has not focused on previously), most importantly without risking any adverse affects on website functionality, speed and SEO!

Many thanks in advance.

Kate