Fairly loud. If you like your car to be relatively quiet day-to-day but have a sporty tone when going for a blast this probably isn't for you.
You'd be lucky to get on a 95db Trackday with one as well. But if you can put up with some volume (Won't use the term noise because they sound really good IMO) they are a good option. Not as loud of J's Racing or Buddyclub exhaust from experience, but certainly louder than a Mugen Twinloop.
Spoon N1 are quite raspy over 3k RPM, I have a full exhaust system, striahgt pipe and then a M2 Motorsport Rep N1 Spoon backbox and that's pretty loud, but I heard the best set up is Aftermarket header, cat / decat, standard center section and spoon n1 backbox.