We've been working with Fidelity Media for over 2,5 years now serving standard banner ads and pop-unders and we find them efficient and responsive. Their CPMs vary from $0.10 to $2.75 depending on performance and they pay on time based on NET 30 payment terms. Using Fidelity Media tags we never experienced any technical or other issues with the ads. But if these would be I'm sure they'll do their best to resolve any issue shortly. If you have never tried Fidelity Media before we would suggest you to do it right away. This is a good network to work with and the best remnant solution to monetize your inventory.
Yep, CPM is fair but fill rate is not very high. they allow you to set backup ads anyway so its no problem for me.