Ok, so basically, what Hawk is saying is that Whirling Reaper is fine as it is. It's a bit more powerful than would be a standard fighter of the same level.
With Acolyte of the Scythe, he finds it poorly written for the reasons he gave. It's kind of hard to put them in layman's terms, but here we go. Basically, it's very unclear, and after I looked at the class myself, I found three problems with the class myself.
1. You aren't allowed to magically upgrade the blunt end of the scythe until you get Weapon Aptitude (another class feature), which contradicts precedents set by Wizard of the Coast (eg: Spinning Halberd from Complete Warrior). If I was running, I'd get rid of this requisite.
2. The bonus feats gained at 1st, 2nd, and 4th level by an Acolyte of the Scythe make the class overpowered, if they are even a feature of the class. They aren't featured in the table, but can be found in the text. If I was running, I'd get rid of these bonus feats, or at least reduce the number.
3. As Hawk said, Scythe Trick is really unclear, but one can guess that it was inspired by the Exotic Weapon Master prestige class in Complete Warrior, which means that an Acolyte of the Scythe picks a Scythe Trick at appropriate levels to be able to use at-will.
In conclusion, I'd allow either class in a campaign (if I allowed homebrew) that I ran with the above adjustments. I hope this helped!