[Arragonis]

EBay chips are resistors in a nice package as T-Vago tapped.

There are piggy back chips - I've seen a lot of them work perfectly and some not, it can depend on the version of the ECU software and hardware.

A reflash is the most reliable way of making a difference but some makers are "locking" their ECUs now to stop this happening - VW I think does this on some newer engines, as do PSA (Peugeot / Citroen).

If you get a mobile company to come and do it to your car they generally reprogram it via the OBD port and will install a "generic" remap, something for more power based on a common and reliable set of values.

The best remap is one done via reflashing and on a rolling road with power and emissions testing at the same time. This is especially true if you are matching this with other mods - say filters or exhausts.

Any company reflashing your ECU should make a backup of what is there before in case you want to switch back.

One final thing, some insurance companies here have been known to check ECUs for remaps if the car is involved in say an accident involving speed - although this is usually where the car is valuable and the driver has a reputation for speeding - e.g. points.