It is hard to answer that question as my car is mainly only Dinan and AC Schnitzer modifications. If I give you my take on Dinan maybe someone else will give their view on another company so you can compare. I have a Dinan S3 540 with lots of Dinan performance upgrades. The negative of Dinan is of course price. You pay a lot of money to have their mods. You can definitely get mods that are cheaper for your car. You can easily spend 35-40 thousand at Dinan in a heartbeat.
What you pay for is what you get though. Years of research and racing experience have definitely paid off. My car is incredibly fast, handles great and no Dinan product has ever broken on it. The service is great. Whenever I need something else done to my car they take care of it right away in a very professional manner.
If you are looking for feedback on a specific part or have a more specific inquiry about Dinan let me know then I can be more specific in my answer. Hope this helps,
Martin