Flat fee companies, by design have little if any vested interest in your success. They collect their fee up front and do the minimum required by the agreement. They work on a volume basis that says if they get 100 sellers to give them $500 each, they've made $50,000 whether anyone sells or not.
They will always have some level of success because each seller has their own motivation. In the research I've done on companies in my area they all seem to have more canceled and expired listings than sold. What this tells me is that while some do sell, the majority either gives up or list with another service, usually a full service one.
Now to be fair, just because another agent charges more and claims "full service" don't automatically assume they are worth it or provide it. "You get what you pay for" should be true but if it were, there wouldn't be a market for flat fee companies.
My suggestion is always seek out the best available representation first, and focus on commission second. A great agent brings value to a transaction and will get you a higher net price, after commissions than a bad agent or none at all. A great agent only wins when you do and will be as invested in your success as you are. If you don't feel they are, find another agent.
Best of luck however you proceed.