Is it a risk to replace the spare wheel with a can of foam sealant in my MG RV8?

I have an MG RV8 with the usual spare tyre in the limited boot space. Considering it would cost about £60 to replace a tyre and I have only had five problems with regards to a puncture in 48 years of driving,...

Should a spare wheel be smaller than the standard wheels?

I have a Kia Niro which I am taking to France this autumn and to France and Spain next spring. I don't wish to rely on the supplied tyre repair kit so have purchased online (not from Kia) a spare steel...