Yes, yes and yes. I use a modified Tuning box (Speedhawk) which pushes her from 170 to 218 horses and from 360 nm to 449nm. I have a friend who can program them...the box as standard would have been 201 bhp and 420 nm...still a good increase. That's a 2.0 JTDm. Completely different animal with the box on. I can turn mine on and off with a remote control. Don't believe the claims to improve mpg....it's BS.....I've used several boxes on several cars...mpg never improved. And if you use the extra power you will use extra fuel. Fitting a tuning box with throw the mpg display miles out so ignore the massive improvement that will show. Measure your mpg tank top to tank top if you really care. Unfortunately this thread will start a argument about remaps being best. But on a direct injection diesel the only way to get more power is by getting more fuel in....diesels effectively are always on full throttle so getting extra air in is not an issue. Inject more fuel get more power. People will say that you can alter boost with a map...but not with a box...which is true to a certain extent (although you will get faster spool up as by product of the tuning box)...but you only need the extra boost if you inject so much fuel that you don't have enough oxygen to burn it....I've not reached that point with a 48 horse increase. Basically that how to get the max out of a diesel...add fuel until you can't burn it...then add more boost (oxygen) so you can and repeat until it goes bang! Remap fans talk about tuning boxes being much the same for any car...and they pretty much are....but then most of the remaps are just generic with no individual tuning for that particular engine. So unless you car had been remapped on a rolling road...you have a generic map for your engines type...might as well just have a box that you can remove easily if you get a problem (I remove mine at MOT time....just to be in the safe side...but I'm assured it would pass) and swap from car to car (often a new lead and/or reprogram may be needed)..can't do that with a remap. So if you want to eke every ounce out of your diesel them get you car rolling road tuned...if you just want a good power increase that you can feel by the simplest method...get a tuning box. Don't buy some of the really cheap ones on eBay though...many are not much more than a resistor in a box....whilst others have questionable reliability (they won't hurt the car but you don't want it stopping in the fast lane ideally)...stick to a big brand if you can.
Ive used TdiTuning, SpeedHawk and RaceChip with success.
....as said above the best ones can be expensive....but only crappy generic remaps will be cheaper...a proper remap with the hours of labour involved and rolling road usage can make it very expensive.....but sure, ultimately this is the best way to get the very best from your derv.... Sure any idiot with a laptop and the right wires can download a cheap generic map to you car (if you have the gear you can find the maps online for free!!)....that should be cheaper.....but you wont get the results that an expert who tunes on a dyno can get....nowhere near.