I have a Soundcraft M12 which is ideal for that back-up situation, plus, as you say, good
for rehearsals and excellent for small events in 'village hall' mode as there are no
groups to confuse novice helpers. I've probably used mine more than all my others mixers
put together ... In back-up mode it stands in for my 32 channel mixer, so there's likely
to be some drastic re-miking going on if I ever need it.