As a Turris Omnia owner I'm pretty satisfied with TurrisOS (based on OpenWRT) and the device overall. However in the case of Turris Shield is different, it is still based on OpenWRT but it is intended for very very basic users who only need a basic firewall and they removed all the advanced options of their other routers (omnia and the MOX).
Turris shield is based on the MOX hardware with 512Mb and maybe some other components missing to reduce costs. It could be very interesting to have a vanilla OpenWRT version for this piece of hardware, since it is cheap (99e vs the 170€ of the MOX) and has a quite powerful processor. I am considering this as a VPN gateway for a small business, but I would prefer Wireguard over the included OpenVPN.