Are they any good?

Ref: https://www.amazon.co.uk/s?k=pc+vacuum

Thinking it's time to dust inside my PC.

I've considered getting one in the past, haven't bitten the bullet yet, they seem to be a good idea being able to blow and suck, not too powerful to damage anything iether.

One of them used in conjunction with the old paint brush method to remove the more embedded dust in the CPU heatsink seems like a good idea to me.

Good plan, I might get one, but will do some research first. 

1/2 inch (10-13mm) dry paintbrush is the best. I have a small Shark vacuum cleaner (called baby shark) with many uses Link

Just make sure you never spin the fan up with the vacuum, it will kill the fan.

Thanks Snowy