It really depends on what you mean by "track visitor activities."
If you just want to track website visitors (page views, sessions, bounce rates, etc.) then you don't necessarily need Dynamics 365 Marketing or ClickDimensions for that. Any web analytics tool like Google Analytics or Matomo can be added to your existing site and will give you all that data. You just add a tracking script to your site and you're good to go.
Where things get more interesting is if you want to track where your leads, customers, and revenue are coming from. So for instance, you want to see a new lead come into Dynamics and know that they came from Google Ads, or from Organic Search, or from a particular Facebook campaign. That's a different problem, and it requires capturing attribution data (like UTM parameters, referrer information, etc.) at the point of form submission and sending it into Dynamics with each new lead.
Both Dynamics 365 Marketing and ClickDimensions have some capabilities here, but they're big, complex tools designed to do a lot more than just lead source tracking. If lead source attribution is your primary goal, I'd suggest looking simpler tools like Attributer.io. It captures where each lead came from (Paid Search, Organic Search, Paid Social, Direct, etc.) along with mopre details one ach channel (so if the lead came from Paid Searchm it would capture the campaign, ad group, keyword, etc). It stores the data in a first-party cookie so it persists as visitors browse around your site, and then writes it into hidden fields on your forms when they submit. That data then flows into Dynamics with each new lead.
Once the data is in Dynamics, you can build reports and dashboards that show things like how many leads came from each channel (Paid Search vs Organic Search vs Paid Social, etc.), which Google Ads campaigns are generating the most leads, how many of those leads converted to opportunities and closed deals, and how much revenue each channel or campaign is responsible for. You can also see which landing pages are generating the most leads, how long it takes leads from different channels to convert, what the close rate is of lead sby channel, etc. Essentially, you get a full picture of your marketing ROI right inside Dynamics without needing to jump between multiple tools.
The benefit of this approach is that it works with your existing website and forms without needing to rebuild anything in Dynamics or ClickDimensions.
