I expect you'll get differing views depending on what that person has fitted, hopefully someone will have fitted both to give you a good comparison however, that person isn't me.

I fitted the Brown & Gammons low coolant alarm and found it pretty easy to do considering my mechanical skills are not the best.

 

Is theirs a complete new expansion tank with the alarm fitted?

 

Yes brand new tank, it's got the sensor built in.

You have to run some wiring to the dashboard but the instructions are pretty comprehensive

 

Over the span of 4 years, I've fitted two B&G/MGOC Spares/RB low coolant alarm kits to our two F and have been very happy with the quality and easy if fitting this particular low coolant alarm kit.

 

Teen water level

1) Drill a big hole in boot.
2) Fit boot rack.
3) Maybe fit cushion.
4) Sit stroppy teen (who is in big trouble) on said boot rack and tell him this is an appropriate subject to shout at at his parents about, if the water level goes down.
5) Fit 2003 Tf suspension. Find pot holey road.

Please note that this is only a temporary measure.

The formulae: The proclivity of teen loss of cool >= assurance of coolant loss.