The problem with faster attacks support is that it gives "increased" attack speed rather than "more" attack speed and the vast majority of attack builds get a substantial amount of IAS already on their tree, which is additive with the support IAS, which means that 44% IAS from the pseudo-link will usually provide substantially less than a 44% increase in effective attack speed.

The shaper pseudo-link IAS mod on this dagger is a hybrid mod that comes with 20–21% IAS. This means you get 64–65% total IAS applied to any skill socketed in this dagger and 20–21% IAS applied to a movement skill like whirling blades. This is actually quite powerful; it's strictly better than crafted IAS as long as the increased mana cost of the linked skill(s) is not an issue. However, if you want to optimize an attack speed-scaling movement skill, you'll prefer a T1 IAS roll or a deafening essence of zeal.

The main reason people dislike it here is that in a true 6L situation where you would consider using the actual support gem, you can usually find a different support gem that would be better for your DPS than faster attacks. In that situation it also doesn't affect your movement skill because the gem is not a hybrid mod. So faster attacks has a reputation for not being good enough to include in most 6L setups. And since pseudo-link hybrid mods are strictly worse than top-tier regular mods, to balance out the benefit of the pseudo-link, only the best combinations are worth much of anything on a weapon.

It's literally more damage than gain % phys as extra lightning damage - level 20 added fire is 44% phys as fire. If you're using it for the link then it's fine. Obviously as a pure stat stick it's not as good, but if you're using this dagger as a pure stat stick you're wasting a lot of its potential. I agree that it's not worth a huge amount, though. Having a big link in a dagger isn't super useful. I guess maybe if you want to put a clear skill there and a single-target somewhere else? Not sure if there are two like that which allow for stat-sticking. For more poe tips and tricks, stay tuned to U4GM. You can choose www.u4gm.com where you can buy poe items cheap.