Out of the two I certainly wouldn’t recommend Shark Performance.
I was talking to Darren (Dazza66) the other day and to be honest he has had a bit of a nightmare with this organisation to say the least.
In a somewhat summarised version (the detail as discussed with Darren was much longer!!)
Darren had taken his car ( a well know Fabia SE “09” plate) to Shark back in June 15 (last year) for uprated injectors to be fitted, stronger headbolts, head skimmed, custom map and aircon fixed.
He was told the work would take 10 days to 2 weeks max.
The Turbo then exploded on the dyno (apparently a boost pipe had failed and had caused something to get into the turbo) – sounds strange to me.
The Turbo was then sent off to be fixed which Darren agreed to pay for (I wouldn’t have)
Anyway it then took until June 2016 – a full year and 1 week apparently for them to finally sort it – I nearly fell off my chair!!
Unfortunately that wasn’t the end of it as when Darren went to drive off after paying a substantial bill (can’t believe how much he paid for the privilege) he noticed the back panel and door had been damaged and had to get this repaired at a bodyshop – which thankfully Shark paid for (that was good of them!!).
Oh and the air-con that was supposed to have been fixed didn’t work and when he took it to a local garage to be re-gassed they said it wasn’t the condenser but the compressor – easily missed I guess!
Although the car (apart from the aircon) was now working well Darren decided he had enough of modified cars and put it up for sale.
Just to add to his woes on the work done by Shark - once he had sold it the new buyer was driving home and the boost pipe popped off – so nice one Shark, seems they really did a good job here.
Anyway based on the above I would certainly steer clear of Shark Performance if it was my choice but I am sure others may have a more positive view/experience of them.
Bit of a long-winded reply to you query I know but believe me this is the shortened version.
So they blew up the turbo, took a year to sort it out, charged a fortune, damaged the paintwork and then it broke down after he sold it !!!
As for Darkside - I have no knowledge of them so can’t really comment but would recommend looking around.