Is it possible to compare Megazyme Kit Units to other companies stated units?

As definitions of enzyme units are very specific, it is not possible to compare them unless both unit definitions are the same.

 
1 unit of activity is defined as the amount of enzyme required to release/form 1 micromole of product per minute from a specific substrate at a specific temperature at a specific pH. 

As the experimental conditions are defined in the unit they are not interchangeable. 

For example for K-AMYLSD, One Unit of activity is defined as the amount of enzyme, in the presence of excess thermostable α-glucosidase, required to release one micromole of p-nitrophenol from EtPNPG7 in one minute under the defined assay conditions, and is termed an Amylase SD Unit. The experimental conditions are defined in the booklet.

In some cases, we do provide a conversion factor to a Unit based on polysaccharide hydrolysis. For example, in K-BETA and K-CERA (Amylase HR), there is a conversion factor which gives a conversion from kit units to International Units on starch which would be a more internationally recognised Unit as it is based on hydrolysis of the 'native' polysaccharide substrate, however unfortunately this is not available for all kits or enzymes.