  We present the first comparison between properties of clusters of galaxies
detected by the eROSITA Final Equatorial-Depth Survey (eFEDS) and the XMM
Cluster Survey (XCS). We have compared, in an ensemble fashion, properties from
the eFEDS X-ray cluster catalogue with those from the Ultimate XMM
eXtragaLactic (XXL) survey project (XXL-100-GC). We find the distributions of
redshift and X-ray temperature ($T_{\rm X}$) to be broadly similar between the
two surveys, with a larger proportion of clusters above 4 keV in the XXL-100-GC
sample. We find 62 eFEDS cluster candidates with XMM data (eFEDS-XMM sample);
10 do not have good enough XMM data to confirm or deny, 11 are classed as
sample contaminants, and 4 have their X-ray flux contaminated by another
source. The majority of eFEDS-XMM sources have a longer exposure in XMM than
eFEDS, and the majority of eFEDS positions are within 100 kpc of XCS positions.
Our eFEDS-XCS sample of 37 clusters is used to calculate minimum sample
contamination fractions of ${\sim}$18% and ${\sim}$9% in the eFEDS X-ray and
optically confirmed samples respectively, in general agreement with eFEDS
findings. We compare 29 X-ray luminosities ($L_{\rm X}$) measured by eFEDS and
XCS, which are in excellent agreement. Eight clusters have a $T_{\rm X}$
measured by XMM and eROSITA, and we find that XMM temperatures are 25$\pm$9%
larger than their eROSITA counterparts. Finally, we construct $L_{\rm X}$ -
$T_{\rm X}$ scaling relations based on eFEDS and XCS measurements, which are in
tension; the tension is decreased when we measure a third scaling relation with
calibrated XCS temperatures.
