It is not recommended according to the installation instructions. The problem is possible sources of interference from the power strip itself or from other devices connected to it (see here https://www.teltarif.de/i...). I have not tried it out, but it is very likely that the data transfer rate will drop somewhat. However, it may still be sufficient for your needs.
Alternatively, these adapters are also available with a (suppressed) socket; you could then plug them directly into the socket and then into the multiple socket there. I wouldn't put my hand in the fire for this combination; to be on the safe side, I would ask the manufacturer.

The advantage is that you plug Powerline devices directly into the socket, without a power strip. :)

Works perfectly. I use it in an old building (built in 1893) over three floors (incl. roof terrace) and via multiple plugs, extension cables and plug-in beams. Works perfectly. Speed loss is not relevant.