I understand your slight anxiety around hiring the designer that will produce the dashboard that would work for your user base.
I don't have any experience with hiring through these platforms neither. Well, because I'm on the other side :-)
Nonetheless, regarding designing dashboards, specific design rules should be applied. Therefore if you are willing to invest resources into a designer, pick the one who is familiar with the nuances of the SaaS business. And the one that understands data visualization principles. You would save a lot of time and iterations.
Btw I've asked the similar question in the fb group dedicated to SaaS growth hacking: https://www.facebook.com/groups/SaaSgrowthhacking/permalink/... Comments that got deeper into problem might guide you to make a decision. Multiple perspectives on the problem were listed below the poll.
Btw I'm curating the collection of UX/UI Best Practices for SaaS applications. List explains tips and tricks to follow in order to ship profitable software. You can find the collection here: http://minimumviabledesigns.com
If you would be interested in cooperation, we can have a chat.