My experience was mixed - I liked that I could control bids and if I didn't like any of the designs that were returned to me in the initial round, it was risk-free because I could get my money back.
The challenge I had was if you need or expect a logo or design that is more than the basics, it can be difficult to communicate the specifics to get those higher quality results.
But in the end, you get what you pay for, and for a more reasonable price point, you're able to get decent, basic design work.
I found better success looking at portfolios on Behance and reaching out to designers whose portfolios I liked. Likely more pricey, but again, all depends on what you're looking for and if it's integral to your product.