This review only covers the 20mm Flakvierling 38 gun which unfortunately is not available as a separate kit from Revell.
The construction sequence is 12 steps found on page 9 of the manual.
The plastic is of a medium-hard consistency and nice to work with. Parts count for the gun only is 55. Detail is quite good and the parts are well
molded and seams are minimal. For the most part fit is excellent though
for some parts it is not the best (e.g. the spent cartridge holder cover (part F97) and the spare ammo clips & their holders). Though not shown in the instructions
the spent cartridge holder cover could be mounted in the open position if desired.
The spare ammo clips (8x part F105) are found
on each side of the gun and are comprised of four separate pieces using a not so good butt join, making their alignment with each other
difficult (see Step 29). Unfortunately Revell has molded them incorrectly anyway. In reality there should be 8 spare clips per side as per the reference photo
(below left) from reference . The kit's spare clips are below right.
As nice as the gun barrels are for injection plastic molding technology they are still a bit too chunky for my liking,
especially the flash supressor cones, so all the gun tubes were replaced with RB Model brass items 72B14.
I added a peg to one of the gun mounting plates to aid with alignment when adding the plates after painting was complete.
I also strongly suggest that the loader's seats with their mounting posts be painted separately and added at the end, unlike what I did, as they are easily
snapped off from the platform they mount to (I leave you to guess why I make this suggestion!).
The shields are excessively thick and look too narrow to my eye. I'm not sure if the narrowness is a problem. I'd suggest the reader check out reference 
regarding their view regarding shield difference. I didn't bother adding any of the main shields and left them off the gun. The shield on top of the mount protecting
the gunner (found on part F95) was also removed.
Some extra detailing was added (refer to the above photographs):
- small handle to side of spent cartridge case (black arrow)
- missing control rod (can be seen on the completed model)
- missing brace between gun mounting plates (can be seen on the completed model)
- grab handles & triangular gussets to front bar (red arrows)
- extensions between body and shield mounting posts (green arrow)
- replaced kit's sight with a Flakvisier 38 sight from Maco 2cm Flak 38 kit (yellow arrow)
- small rectangular panel with three small holes located on the front of the spent cartridge collector. Not sure what it's purpose is, maybe a vent of some sort?
One thing is for sure though. After reading through the comments & checking the pictures found in reference  it appears that this Revell
kit is a downsizing of the 1/35 scale Trumpeter Flakvierling. This is particularly evident when looking at the shield dimensions and the platform under the loader's seats.
A very nice offering from Revell. It does have a few problems but they don't detract from the overall quality of the kit. Compared to the competition in
injected plastic, the ancient Hasegawa kit and the
more recent Military Wheels kit, this model is vastly superior.
Note: The 2cm Flakvierling 38 used for this Revell kit was originally designed by MACO.
The same parts are found in the MACO set 7212 (sWs) while a subset with parts for the gun only is found in kit numbers 7214 (Flakpanzer III "Wirbelwind")
and 7216 Flakpanzer IV "Möbelwagen").
 German Medium Flak in Combat, Werner Müller, Schiffer Military History, Westchester 1991 ISBN: 0-88740-351-4
 German 20mm Flak in World War II 1935-1945, Werner Müller, Schiffer Military History, Atglen 1995 ISBN: 0-88740-758-7
 German Artillery at War 1939-45 Vol.1, Frank V. De Sisto, Concord Publications, Hong Kong 2007 ISBN: 962-361-143-9
 German Artillery at War 1939-45 Vol.2, Frank V. De Sisto, Concord Publications, Hong Kong 2008 ISBN: 962-361-144-7
 www.perthmilitarymodelling.com (Dragon vs. Trumpeter 1/35 scale Flakvierling comparison)
Review sample purchased by the author.