Read the hammer pack sticky. It shows the variations of the PS90 and FS2K hammer packs.
There are some minor variances but generally, this is the way it is.......
There are two generations of the FS2K hammer packs. They are both off white/light brown. The first generation has the auto sear on the front of the pack. The second generation looks and operates exactly like the first generation except there is no auto sear on the front of the pack. There is only one generation of the F2K hammer pack (that I know of) and that is the FA pack.
There are 4 generations of the PS90 hammer packs. Three come with auto sears, one does not. Of the three, one has a hammer that is notched higher making the auto sear all but useless. The remaining two are the Gen 1 and Gen 2 packs. The Gen 1 pack is all black with a dark green sear (not auto sear - there is more than one sear in the hammer pack) and the Gen 2 is a mixture of black and gray parts.
A Gen 1 pack is a rare find for a FS2K and it can be sold for as much as $1K on Gunbroker and yes, there are some people that are willing to pay that amount for it. The Gen 2 pack that you can buy from Browning Parts cost about $40 to $60. So some people will buy a Gen 2 pack for their FS2K and sell the Gen 1 pack to recoup some monies.
Like all hammer packs, the auto sear is necessary to make the firearm go bang real fast. It has also been noted although unconfirmed, that if you send in your Gen 1 pack (FS2K) or Gen 1 or 2 pack (PS90) for repair under warranty, the firearm will be returned to you without a pack with the auto sear in it. I have heard of it not happening and I have heard of it happening.
Most people who have the Gen 1 FS2K pack and/or the PS90 Gen 1 or 2 pack, will buy a seconday pack to put into their firearm should they have to return it to FN for servicing, that way you ensure that you will always have your Gen 1 (FS2K) or Gen 1 or 2 (PS90) hammer packs. I have spare packs for both my FS2K and PS90's for this reason.
All hammer packs no matter what generation, operate as they are meant to. You pull the trigger and the firearm goes bang, ONCE.