I must say that used "sensibly", I find my Kreg K4 both invaluable and very well made. I wish I had known about these things sooner, when building up the MG Midget kids pedal car project (see "Longest Ever ...... ?" write up now in progress in the Project section here).
But I do dislike the Kreg screws (both in terms of price and - here anyway - relatively poor availability) but unlike some other members here I have never tried the idea of using a "normal" CS or RH screw plus washer.
I'm not so sure (despite tests I've seen) that Kreg joints are weaker than, say, dowel joints, but to me the idea of substituting normal screws with the proper screw is just a poor and potentially weaker "engineering" solution, sorry. Perhaps these tests showing weaker joints didn't use the proper screws? Dunno.
The other thing I don't like about Kreg's own screws is those "stupid" Robertson square drive heads. They cam out FAR too easily (even with the official Kreg driver bit). I know Eric (the Viking) likes these, and Eric, I've seen you post before that these (silly IMO) heads are found in aviation. I do NOT want to start a "fight" here, but must say that in my whole aviation career (started 1961, ended Dec 2014), throughout that time I've never seen a square drive screw/bolt head on any aeroplane. But all my work has been with military or "big" aircraft, never with small, GA (sports/private) machines, so perhaps they appear there? Dunno.
Anyway, thread drift, sorry. IMO, used for its proper purpose, I rate my K4 highly, and as opposed to using a CS screw and having to fill the depression afterwards (for an invisible joint) the pocket hole idea of a piece of dowel glued into the hole then cut off flush is IMO a definite plus. (But I would NOT pay Kreg's prices for their own plugs)!