The surgery is always going to carry risks, despite some doctors hailing the advancing of limb lengthening technology with internal nails as something that will make the process no big deal. At most, internals will increase your comfort during the lengthening and consolidation process compared to externals, and will minimize external scars (which is mostly an issue with femur lengthening), but it will still come with aches, pains, sleepness nights, etc. I don't think there's a surgeon yet that underwent cosmetic lengthening themselves, so everything they can tell you is either based on word of mouth from their patients, or just what they've read based on published studies.
Absolute worst case scenario, you get a complication that kills you. Second worst? Probably limb amputation. Maybe your bones just have incredibly poor regeneration and never join back together, requiring multiple other surgeries to fix. Or maybe you get permanent numbness in one or both of your limbs. Maybe it's just as simple as a permanent feeling of tightness in your hamstrings or calves that never goes away, or your balance is considerably weaker. Or maybe even after you hit that 6 foot mark, you notice absolutely no difference in how others perceive you and then you start to wish you invested in something else with all that time and money.
Compare what you stand to gain from hitting 6 feet to what you can potentially lose.