I've used Cementone, which is similar to Geofix and about £30 a tub from Screwfix, which tends to be the cheapest I've found it.
To be fair it's OK and very easy to use.
Bad points though, it works out very expensive, isn't the most resilient and for your job matching the colour will be tricky.
If you are able then best mix your own and point up the bits that need doing yourself.