Hi there, mate! Cheers!
They are all relly invasive. There are internals and externals, I would say internals go inside your bone, but they give less scaring, infection and other things compared to external. Internals are the most new ones (precisa and the wonderful Stryde). It's a fact that the more you length the more complications can occur, the longer the rehab and revocery will be and a higher chance of not going back to fully 100%. But, it mostly depends at your body, as flexibility, health, and etc. There some people who do 14cm and are completely fine and some who did 5cm and are not the best now.
The best way nowadays is using stryde, but it had a recall due to some issues, but should be released again. Stryde and Precise are almost the same, the difference is that stryde can tolerate much more weight bearing, and that means you have a faster recovery, faster bone consolidations and rehab is easaier.
Doing one segment (tibia or femur) is less invase than doing both segments (tibia and femur) of course.
Won't extend more here, hope it helped, but I can't say which is more invasive, cause they're all REALLY invasive and involves breaking a bone. The lengthening amount does matter a lot, but your determinance, doctor, fexibility, health, PT, rehab, etc matter a lot more!