Crash tested car crates, does anyone recommend?

Does anyone have one of those crash tested car crates? I am currently pondering whether to buy one. The main reason being as it is the only ready made crate that will fit in my car, which is a large 4 x 4, but not big on boot space! (~stupid design!)

My choice is between that crate or a custom made tailgate guard.

I need to fit in an adult 34kg flatcoat ret, and a 6 month golden ret currently 21kg,(who i expect to reach about 30kg). I just want to give them the most space but in a safe and secure way, (for them and the passengers!)

Any opinions would be appreciated, thanks.