I installed one from Forest Wind, around RM1.4k (can’t remember exactly).
The DC motor died after about 1.5 years, but they honoured the warranty and came to replace the faulty motor.

Not sure if I was just unlucky, they told me it normally lasts around 8 years+.
It does improve ventilation a bit, but honestly, if you have the budget and time, I would recommend spending on proper thermal insulation instead. That gives a much better result overall

I think for burglary access is subjective.
The installation require a hole probable 10inch wide, or a replacement of 1 or 2 roof tiles. So it depends how accessible is your house roof.
It will not likely be bolted in but clipped, and silicon gel to prevent water flowing under.
and it should be installed at the ridge/apex of a roof ( the tip point) and under  the Ridge flashing ( metal sheet that runs across) to let the rain water flow over the flap of the ventilator bottom