Re: Five-Seven
I have both Five-seveN and PS90. They are a hoot to shoot! Superb accuracy with both weapons. Ammo is not that unreasonable - you can find the SS197SR (40gr V-Max) for ~ $18/box (50 rds); SS195 is ~ $22. Regarding flash, it is a rifle round - lots of powder burning beyond the almost 5" barrel. I personally like the grip texture, angle, and size. Typical Belgium, it does have a magazine safety (bummer), which is easily disabled without much trouble.
I look at these as investments - picked them up before they were popular. It's interesting they are maintaining value. You don't find "deals" on either one - new or used unless seller is in a bind.
Go for it!