Non Zed emergency tyre kit

[obewan]

Appreciative of some advice on tyre repair kits
In my wife's new (used) car (with no spare), the tyre kit consisting of a compressor and sealant has been removed

So my question, do I buy a replacement - on E-bay for about £30, or just a tin of expanding foam
Which is best?

Indeed are they different?
I've assumed the sealant type does just that and you then need the compressor to re-inflate the tyre
Whereas the foam expands to re-inflate the tyre to a degree and I may need a pump to top up

Thanks in advance

 

[srhutch]

I bought a BMW mobility kit off eBay for my 1 series when changing from run flats.