When deploying memcached on the IDP test instances I noticed that we puppetise the systemd service. But leads to a number of potential breakages during updates, if a new memcached package is deployed, the puppetised version gets overwritten until the next Puppet run.
The memcached class already uses systemd::service, so we can deploy our specific ExecStart call via an override.
This would also allow us to benefit from changes to the memcached unit in Debian, the version present in the stock deb ships various hardening features which we currently miss.
Also, memcached in stretch and later ships a systemd-memcached-wrapper which simply points to /etc/memcached.conf, so it would also be an option to switch to that and possibly no longer customise the systemd unit at all.