Turkey is an F35 partner and plays a role in the manufacture of F35 airframe components - so I'm presuming security is not considered a huge issue.
The £100m deal is not new - the project was started in 2010. There is also talk of tech transfer of the EJ200 for the project. The plan is for a super-cruising F-22 lookalike - so this might be a very interesting project to get involved in.
Great darts by TM for flagging it up straight after holding hands with POTUS. We've heard nothing but EU propaganda up until now about the UK's likely outcome in the Article 50 negotiations. A few more examples of how the UK is free to trade without garnering 27 signatures over 10 years might inject some realism into the process. Turkey was a particularly smart choice as the EU has been shutting it out.
As far as the moral high ground about who we trade with goes, TM has specifically stated that we will not make the same high-handed mistakes as TB made in trying to enforce our own model on everyone else. And if we are on friendly terms - we have more chance of discussion and persuasion.