...
May need to do additional finishing work after vacuum forming a part
Vacuum forming cannot produce a very detailed part
Clear or light-colored parts can show debris from the mold
Sources:
https://www.pacific-research.com/the-advantages-and-disadvantages-of-thermoforming-prl/
https://www.pacific-research.com/the-advantages-and-disadvantages-of-vacuum-forming-prl/
https://www.universalplastics.com/what-is-twin-sheet-thermoforming/