I was very excited when this card came out to try him out in my 4-1-2-1-2 narrow formation. People that are familiar with it know that full backs attack quite aggressively in this formation even on balanced settings. I've had UCL Florenzi run down the other wing for quite some time so I know what it's like to have an attacking full back and I was excited to replace my defensive Alex Sandro with an attacking minded Salah.
To start off the only chemistry styles you should be using are Sentinel and Backbone. Personally I shoot more with Salah than I cross so I went with Sentinel to fully boost his defending. He does the job well: Has the pace to keep up with fast wingers, decent strength to hold off attackers, wins a fair amount of aerial duels and just an overall solid full back not factoring in the attacking prowess he brings, which is unmatched by almost any full back. You'd be looking at TOTS Marcelo or Prime Moments Roberto Carlos and even then I'd make a case for Salah being the better attacking LB out of the three, mostly because of his high finishing in combination with excellent dribbling and passing stats.
However, I do have to say that defensively I think there are many better options out there. If you are playing with wingers or just value defending more than attacking from your full backs you should not be considering getting this card. After using both 86 Alex Sandro and LB Salah for a lot of games now I'd argue 86 Sandro is perhaps even better defensively than Salah. If you're looking for liverpool links and want a defensive LB you should get an IF Robertson.
To sum it up this really is a niche card to have more options for those of us who attack aggressively with our full backs. Those who do will get some real enjoyment out of this card, but those who don't shouldn't be considering ever getting LB Salah.
Attacking unmatched by any full back
Decent defending with the right chemistry style
Perfect for formations where the full backs cover the entire wing
Low defending stats for a 300k 90 rated LB