Just my $.02
Not a fan of the concept of increasing bat speed as the end all to better hitting. My focus would be on swinging as heavy a bat as I could and still have barrel control. Light bats have destroyed to many swings, created armsie swings vs using the body, so increasing MOI is now the thing. Swing fast, swing with intent, so when you run into a baseball (1 in every 20 at bats) you hit a bomb.
In my opinion training would be all heavier than my game bat. Not for bat speed, but for better bat control. You don't have to swing hard to hit the ball far. Better contact produces a further hit ball than fast poor contact. There is an epidemic in today's game of thinking being a .250 hitter with more homeruns is better than a .350 hitter with fewer. The problem is that there are too many .250 hitters who still can't hit homeruns.
As my son's hitting coach says, if you can't hit .400 in HS baseball, you can't hit. That might be a bit much, but I get his point and don't disagree with it.
To me, by chasing bat speed, the swing is in danger of becoming a pull swing, potentially ripping the shoulder or front elbow out to increase velocity. Feels great, feels strong, but... You would have to be really careful to mind that in order to increase your bat speed without cheating in that manner. Which of course then causes issues like, casting, running out of barrel, not getting extension, poor direction, exposes the outer 1/3 of the plate, rollovers, etc.
Of course the pull swing is an inside pitch swing and has it's purpose, but it isn't an every pitch location swing.
Don't lose a good swing with good direction, chasing bat speed.
If you are looking for weighted bats, over and under load. I'd simply buy used bats or cheap bats that weight more.less, unless you are already swinging a 34" but taping pennies to the end with hockey tape works. Those weighted bat systems can get expensive for no reason.