Thanks for the update Harry. Sorry it wasn’t successful and didn’t live up to Autoglym’s claims.
Whether you just get the bonnet polished or the whole car I think depends on the condition of your paintwork. Being black, it will show imperfections if there are any much more than, say a white or silver car, in which case considering getting the whole car done might be a consideration.
When I’ve ever needed to machine polish localised areas of paint work to remove marks such as bird poo etching, just doing the affected area has been fine. I’d say if your paintwork’s in generally good or very good condition with minimal swirling or imperfections, then getting the whole car polished because of bird poo etching on the bonnet is probably overkill, and just getting the bonnet done should be OK.