I started using these brushes the day I bought them and haven't stopped since. They are not just simple brushes but are carefully crafted presets that leverage the full power of the Photoshop Brush Engine. I've had no regrets passing my $13 to Kyle for his efforts.
My one problem with them is how Kyle chose to name them. Example: "Kyle's Paintbox Fat Fun 100" This seemed fine at first but when scanning through an expansive list of 100+ presets I'd much rather see something more functional: "Oil - Filbert - Dry". I'm in the process of slowly renaming them for myself and they will become even more useful.