Max
There's been a ton of professional work done with big hybrids.
Safety and convenience are the big motiovators for large professional hybrids. A hybrid theoretically should be able to generate the specific impulse of a liquid motor, with the convenience of a solid motor while at the same time have unparelled safety since the motor can be shut down simply by stopping the oxidizer flow. If the structure should fail, the chance of an explosion due to fuel oxidizer mixing in a liquid is eliminated since the fuel is a solid.
The latest trend in big hybrids is to use a parafin wax as the fuel (essentially solid RP-1), the theoretical specific impulse is virtually the same as LOX/RP-1 or NOS/RP-1.
Try a google search on "hybrid rocket motors"
NASA Marshal has fired a 24" hybrid.
https://www.cnn.com/TECH/space/9908/19/rocket.test.1/
Check out Scaled Composites Spaceshipone and the hybrid competition between Environmental Aeroscience Corporation (eAc), and SpaceDev.
https://www.scaled.com/projects/tierone/index.htm
https://www.hybrids.com/about.html
https://www.spacedev.com/newsite/templates/homepage.php?pid=2
https://www.stanford.edu/dept/news/report/news/2003/november5/rocketwax-115.html
The most serious problem with large hybrids is the uniform distribution of the oxidizer throughout the central core of the solid fuel. Unless the distribution is uniform, the specific impulse suffers and is more similiar to that of a solid vs that of a liquid. The oxidizer injector design is the major stumbling block with big hybrids.
Nitrous is not cryogenic so it offer handling advantages over LOX with a 10% reduction of specific impulse. A 70/30 PE/LOX hybrid has an Isp ~ 295 seconds vs a 90/10 PE/NOS hybrid with and Isp ~265 seconds. (PE is polyethylene which is thermoydamically equivalent to wax.)
Inverse hybrids have also been investigated, but they offer no advantages, and have several disadvantages over the conventional hybrid design. The packaged volume of an inverse hybrid is greater than a conventional hybrid since fuels have a lower density than oxidizers, and an inverse hybrid is not easily shut down since the hot oxidizer will continue to pyrolize and generate oxygen which could fuel a casing burnthrough after fuel flow is stopped.
Bob Krech