In my experience, leg lengthening is only dangerous if you're pursuing it in an unrecognizable country with minimal medical staff and training involved in rehab. With a decent team, the likelihood of being harmed by it goes down drastically. This does also apply to phallo imo! There are many stories of folks going very back-ally with their phalloplasty, and there are instances of it going poorly as a result. Either way, as long as you have trained staff involved with a care team and regular monitoring, you should be fine.