I've been in 135 for 10 years and info in the link above is pretty accurate.
Southampton Det only opened recently, but I do know the TA Centre and it's not bad. It's co-located with several other units if you fancied a transfer later on etc.
There is probably less emphasis on combat engineering and infantry stuff than most Engineer units because we are a specialist unit.
The road to Geo Tech can take a while, depending on how much time you can get off work.
To be a Geo Tech you will ultimately need to be familiar with computers etc. The unit will sponsor you through a European Computer Driving licence (ECDL) if need be.
After any Combat Engineer training, you will need to do a Class 2 GID (Geographic Information Dissemination) course at Hermitage. It's a 2 week course and is a prerequisite for anyone in the unit. It covers most of the basics of GID and also covers some GIS (Geographic Information Systems) in the training.
After Cl 2 GID, your can either go for Cl 1 GID, or go down the GIS route. Either way, get to this level and you'll be very popular if you volunteer for Ops.
As the info in the link says, you could also go the production (printing) route, gaining experience on great big printing presses or go down the mil survey route.
There are a few other routes you could probably go down, but the ones I've mentioned are the maiin ones.
The unit is keen for everyone to get C+E, provided you've established and proved a commitment to the squadron.
Lastly for now, if you like your AT, especially skiing or mountain climbing, 135 is your unit.