There shouldn't be problems. As long as you maintain your jailbreak. With respect to battery draining, more or less your battery will drain a little faster while tethering, which is the case for all devices pretty much. As for personal information, Malware and Spyware are VERY rare. There're so many different sublevels for the iOS with their sandboxes, so if they're targeting your phone directly, they have to try really hard to do it, or they'll have to physically have your device to bug it
As per tethering, make sure that you choose a tethering app that spoofs data usage properly if you don't want to pay for the monthly tethering fee. In some cases, if you call up a rep from your carrier and they see that your data pool is large enough and they're having a good day, they'll open up the tethering port for you and void the monthly payment
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