Level 3 Lightweight 4E Life support
There is no reason whatsoever to use a 4E lightweight life support unless it's due to lack of money, which can soon be remedied and especially be remedied before starting to engineer it.
The module letters usually mean:
E: econonmy. cheap. No other redeeming features
D: lightweight
C: whatever
B: robust, heavy
A: top performance
For an explorer, the choice is usually between D for lightweight or A for performance. For the life support, the mantra was fora long time to go for D, since there was no need to get the 25 minutes life support time you could get from an A rated life support. If the canopy was smashed (or life support was disabled due to any other means), you were dead.
That slightly changed with field repairing your ship and specifically the "repair&reboot" option, as that one disabled the life support for the duration - and the oxygen depletio9n was cumulative.
Since we now (well, some time during 3.x) can synthesize oxygen for the life support, that changed drastically - now you can make your way back to civilization even with a smashed canopy, as long as you can keep synthesizing Oxygen (some people did, at least one under the wings of the Fuel Rats/Rock Rats/Hull Seals, who helped to supply them with synthesis materials). And there's a difference between having to synthesize every 7:30 minutes (D rated, or even 5 minutes for E rated) and 25 minutes.