I am currently running a pure dex and spear/poleaxe/reaper build. I just reached zigurat/ruined temple, where this class get a huge increase in interest (unlock rusted greatblade in zigurad + find a second reaper on ground in ruined temple)
This class has quite a few balance issues honnestly. The starting reaper is too strong in early game. It has incredible base damages, thus you can focus on increasing your willpower a bit first, so you can pull up deadly combos. Early game boss and ennemies are completely obliterated. Then the weapon fall behind mid game, because of low scaling.
The problem is that there is no decent upgrade. War scythe is ok, and is lighter, but deals very little aditionnal damages. Red eclipse is the same, but is very very heavy, and is only available just before Hagger Cavern, where slash damages are quite useless. Forget about purifier, it is for wis builds. Rusted greatblade is just a worse version of the starting reaper : twice as heavy, lower base damages, same scaling. Gravedigger is even worse, its damages are even lower, plus it doesn't get a lot from buffs. Finally, Saltreaver is only available super late game.
However, even if the balance of the class itself is a mess, this is a very fun weapon to use. I would say that a reaper makes the game balanced (except in early) : I don't feel that I cheese the game like when I play some STR builds, but I don't feel too weak like when I play the left side of the skill tree. Since it has high base damage, I can also get a good armor without throwing too much dps away.
Also, this is very nice to have such a good coverage of blunt/slash damages. You can play reaper only and be able to deal with any scenario (not until zigurat/ruined temple however).
Finally, I guess that this class might be very interesting for a wisdom/dex builds. It has huge base damages and poor scaling, which maximise the effectiveness of blessed weapons. The purifier is a holy weapon accessible quite early. There is even a weapon with MP leech ! (well, I don't think MP leech is worth it in this game, but at least it is here).