Theres no 100% when tuning Im afraid. I assume you are manual ?
Depends how many miles and how your car has been treated to some extent, along with the remap (amount of gain ,plus graph of delivery)
Any decent remap will give you good bhp/torque gains (torque especially which kills clutches/flywheels)
Most later cars seem to get away better with a stage 1 (either due to age or improved clutch parts)
Theres also a difference K03 GTI vs K04 Edition 30
The K04 cars tend to remap to higher values and therefore tend to have more issues sooner.
for your car its a K03 (lower low rpm torque hit , easier on clutch) , but its 2005 , so you may have an earlier version as well as many more miles (?)
consider it all as a matched set , flywheel / clutch plate / pressure plate / release bearing.
If one part is marginal or a weak link , youre going to get clutch slip.
I say talk to your tuner about it , but get the remap and budget for a clutch in the future just in case.
Also you want to consider 'respecting the clutch' once remapped , so no low rpm pulls (try and change down first) , no traffic light grand prixs etc, these may prolong its life.
Its a 2005 car , so you may also want to consider suspension/bushings as any power increase is going to highlight any age related weaknesses.
In remap terms, REVO is tried and tested but given you are in Finland support may be an issue?
The local shop remap, is it their own map ? or have they bought it in?
normally on this forum we would say , stay away from 'custom' remaps. But you may find its a well known name under the covers.
Anyone else had the remap locally that you can talk to?
They may be better for aftersales care and support if you hit issues.
Id say just go for it , dont worry too much about the what if's, if it breaks you'll have to fix it
Drive it to enjoy it