Ask HN: How much do you spend on Adwords/others, and is it effective?

Now that I've got some concrete sales for one of my products, I'm thinking about spending a bit on advertising for my consulting firm (specifically one product: https://osrec.co.uk/products/heavymetl).

My question: is it really worth it? I ignore pretty much every ad I've ever seen online (apart from one that gave me free Adwords credit :p), so I'd like to gather some opinions/anecdata to determine whether this is a worthwhile thing to do, and how much I can expect to spend before reaping the benefits.

Thanks in advance for any input!