So there's fairly consistent advice across this forum to concentrate on taking more 'stealers, rather than upgrading them... But personally I'm just not convinced!
For example, in the current list I'm working on I have a 240 point 'stealer unit... I'm deciding between either 10 x EC and ST or 12 with just EC...
The unit of 10 will get 30 attacks a turn, the unit of 12 only 24... Are people really saying that the extra durability of having 2 extra 'stealers is more than the extra lethality of 6 attacks per turn...??
Somebody's gonna have to show me some calculated counter examples before I'm convinced...!
It looks a bit different after some shooting:
Lets say the enemy is going to kill about 6 of your stealers before they charge.
Now you must compare 4 ST EC (16 attacks) stealers to 6 EC stealers (18 attacks).
Thats a pretty good argument to me to drop the talons and get the extra bodies.
Dont forget to factor in subsequent rounds of combat:
Assume that after the charge the enemies will kill 2 more stealers in retaliation.
Now you have to compare 2 ST EC stealers vs 4 EC stealers.
(For giggles, we can compare non-EC stealers, of which you would start with about 15. sadly, twice as many die to shooting, so you would end up charging with about 3 of them)
In summary, the scything talons are a bit overpriced when you factor in enemy shooting.
I would probably use them if they were a 2 point upgrade. I would also use them if I didnt think the enemy would
be able to shoot them before the charge. in my typical games, I think EC stealers work out best.