I can't comment on the kits but the way my friend installs windows on his cases:
1.a) Goto Home Depot (or other hardware store), buy 1/8-1/4" plexiglass in required size
b) Goto Beer Store
2. Go home to workshop
3. Power tool time
4. Cut hole in side panel
5. Cut plexiglass to fit
6. Rivet plexiglass in place on side panel
7. Paint