[Contact Widget] CTA BUTTON PLUG IN OR BUTTON DESIGNED WITH CUSTOMISED CSS?

Hi!

I have a blog news and recently we hace decided to launch strategic campaings through newsletters. Since we started the project in 2016 we have received a lot of traffic but we didn't kept track of our visitors. We haven't gathered any information and now, since the the site has progressed we want to have more control and we are hesitating about which would be the best and less intrusive option.

Therefore, before going for pop ups or slide in, we want to try CTA buttons like these ones:

https://www.market-inspector.co.uk/web-design

https://www.shopify.com/online

We wonder though if is there any recent trend about is the most UX efficient design and whether a customised button would be more accurated to keep track of the interaction than a plug in with UTM links. Moreover, are there CTA plug in buttons in wpmudev?

Thank you for your help!