Use the Purpleice. I haven't seen the so-called Prestone issue. Even those some of the below mentioned additves work best in straight water, they will still work in a 50:50 blend.
All engines have hot spots. Whether those hot spots are causing issues is something that companies are cashing in on.
Another problem is that most people don't have clean coolant. They read their owners manual and enjoy the neglect it allows.
For future maintenance, just use that 50:50 mix. Practice a yearly maintenance program. There is no need for additives if everything is working correctly.
I would never recommend or even consider running straight water even if the weather allows. I've seen too many, storage unit heat failures, trips to the mountains, and freak cold weather spells, which can kill an engine.
I also don't see too many companies advertising the strength or life of their additive packages. I've seen scale and corrosion in vehicles run with straight water with these additives. They need more frequent maintenance. If you don't believe me, contact your additive company. Have them prove that their product will provide the same long term anticrud performance when used with straight water when compared to my additive free 50:50 mix. Most provide additional protection to the antifreeze mix and will need higher doses, or other additives, for straight water usage. Antifreezes/coolants are tested to OEM, SAE, or ASTM standards. Are any of your additives tested?
I have no problems running any of the additives(wetting agents, antirust, pump lubes) from Prestone, Zerex, Redline, RMI, Lubegard, RoyalPurple, BMR, RadiatorRelief, Firefreeze, Problend, CRC, KwicKool, Gunk, Motorcool....But, I don't see the need if your cooling system is working, is maintained, is at a ~50:50 concentration.
If weather allows, consider leaning out the antifreeze to 25% with your product of choice. But, beware that you will require more frequent maintence to prevent scale and corrosion, that you will need to read the directions and dose your product properly.
Another problem(vehicle dependend) with running straight water in warm climates is that your A/C can freeze the water in your heater core, dependent on HVAC plumbing.
So, please run some antifreeze. Even a 25% blend, with your additive of choice, has many benefits you might not see right now. Hindsight is 20:20.