I would stick with using straight up sugar instead of equal or splenda for PWO. By using artificial sweetners you're basically selling yourself short on multiple fronts, the most basic is the calorie consumption, the second is the insulin response that you get with the sugars.
Also, in order to get a decent amount of sweetner out of those packets, you'd need like 40 of them per PWO drink... that's a pretty high dose of aspartame or sucralose to be ingesting multiple times a week.
Even if they say that it doesn't cause cancer, odds are taking that much in per day isn't as safe a bet for your health vs not injesting that much artificial sweetners.
a cheapo alternative is gatorade mix, you can get a pretty big tub of this stuff at costco or normal size things of the powder at the grocery store... don't forget to mix in some protein (this will taste aweful!)