The 2.4Ghz one works well, although obviously slower than the other.
The 5Ghz one is a bit problematic, because sometimes it is not visible to devices. The happens with a diverse variety of devices, a Dell XP laptop, a Microsoft Surface laptop, a Huawei phone, a One Plus phone, and even with an LG smart TV, even if all these devices are in the same room and as close as 1 meter from the router.
The SSID is simply not visible when the device starts and tries to connect to it, it only shows after a few minutes, even happens in my laptop when it comes back from sleep mode. Sometimes when it shows is with a poor signal level, even if it seems to improve later.
What can be the reason for this, might it be a problem with the router?