So, I'm going to talk about Wych weapons. Those of us who are familiar with the Dark Eldar codex are well aware of the three different weapon upgrades available to squads of Wyches. Those being Hydra Gauntlets, Razorflails, and the Shardnet & Impaler. A lot of the net-lists out there seem to always opt for the Shardnet & Impaler. Here's why I believe that's wrong.
Before I get too far into this here's a quick summary of what each weapon offers;
Hydra Gauntlets grant an extra D6 attacks, each turn, for having two ccw's rather than the normal +1.
Razorflails allow you to re-roll to-hit AND to-wound.
Shardnet & Impaler reduces the attacks of each model in base-to-base contact by 1, to a minimum of 1.
Two of these upgrades are offensive in nature while the third is defensive. When choosing how to equip your Wyches you need to consider how you're going to use them. Will they be an aggressive unit? Or. Will they stay home and act and as a counter-charge unit to keep the enemy away from your lines?
If you're using them a counter-charge unit then, by all means, equip them with the Shardnet & Impaler. Being able to reduce the effectiveness of an enemy assault is a fun trick that can agitate your opponent to no end. But if you're going to use them as a counter-charge unit I believe you've missed the point of the unit entirely. If you want a unit to sit back on your objectives just take Warriors in a Venom. They're cheaper and can lay down a lot of splinter fire.
Wyches are an offensive unit and to use them in a defensive, counter-charge, roll is a bit of a waste.With their base initiative 6, combat drugs, and a fair number of attacks they can destroy your opponents battle lines before they even strike back. If you're using your Wyches in this capacity then you'll be deciding whether to use the Hydra Gauntlets or the Razorflails.
Like a lot of people, I just assumed that the Hydra Gauntlets would be the better purchase because of the bonus attacks you get each turn. I quickly realized that this was not the case. Hydra Gauntlets can be amazing if you're able to get the strength bonus from your combat drugs. But with just a 1 in 6 chance I'd rather invest those points on the Razorflails. Why? Take into account that there are a crap-ton of Space Marine armies out there and you realize that Wyches are only going to cause one wound for every three hits in combat against these armies. Since the Razorflails give you a re-roll to hit as well as to-wound your odds of not only scoring more hits goes up but those hits have a higher probability of causing a wound. And we all know that the best way to kill Marines is to drown them in armor saves.
In summary, if you're going to use your Wyches in more of a defensive roll then you'll want to be using the Shardnet & Impaler. This will lock down your opponents offensive units in combat for a long time. Whereas if you're going on the offensive with them (as you should) take the Razorflails over the Hyrdra Gauntlets. With all their re-rolls they are a far more reliable wound generator than the Hydra Gauntlets. Since the Dark Eldar rely on their speed to win games being able to cause as many wounds as possible in each round of combat is very crucial.