The Gunk ultra degreaser is a water-based product. It is thus a detergent rather than a solvent. It is very similar to generic traffic film remover. A reliable product with the same chemical composition is Screwfix' No Nonsense degreaser. These are both relatively odourless.
The next step up from this is a solvent-based emulsifiable degreaser. It is a lot better on really greasy stuff. It can be washed off with water (the emulsifiable bit) and disposed of down the drain. It leaves a slightly oily film on parts after rinsing, which gives a little corrosion protection. Everybody and their mother sells it (Rye Oils, just as an example
Degreasant - Rye Oil come in and see what we have on offer). It smells very solventy and lingers on your clothes. JennyChem sell an odourless version (no experience of it).
Above that are pure solvent degreasers like kerosene (paraffin), heating oil, diesel, petrol, cellulose thinners, white spirit, etc. These cannot be poured down the drain.
For a really good clean, use the solvent-based emulsifiable one first, rinse with cold water, followed by a hot wash with the Screwfix one (around 4:1 dilution). Hairdryer or hot air gun to dry and then a corrosion protection spray.