I'm looking for a device with a directional antenna so that it can cover outdoor clients over a few hundred meters. Must have 2GHz and hopefully also 5GHz. Should be easy to install OpenWRT (ie. one step process) using either TFTP or web gui based install. And reliable!
Is there anything anyone can recommend?
This will be used by people who do not have regular internet access at home.
Just get any supported router and buy a separate antenna. You'll need to choose one with an appropriate beam dispersion, depending on your needs, as they vary quite widely.
Some of them are pretty expensive. Zyxel make a few.
These are usually called CPEs (Customer Premises Equipment) since the primary market is to mount them on houses as the customer end of a WISP (Wireless Internet Service Provider) service. But with OpenWrt they can also run as a regular AP and serve endpoint devices at moderately long range.
Examples would be Ubiquiti Nanostation series or TP-Link CPE220.