The Swedish & Imperialist box sets are both based around the same basic sprue as the ECW boxes. Each set has 3 standard sprues and 1 plastic command sprue. They each then add 5 metal figures, some different hats & helmets and musket rests.
The Swedish set has 2 extra armored pikemen, crouched to receive cavalry charge. And 3 brand new command figures, the command figures are a little more 'european' looking perhaps than previous ECW but are in no way in my opinion too extravagant to be in an ECW army, (bear in mind plenty of TYW veterans fought for both sides in ECW) these come with alternate arms and hats. The set come with enough helmets to put all of your troops in helmets if you wish, I used a set of these for part of 1643 Parliamentarian army and just put all the pike in helmets and used a selection of the usual hats on the musketeers, I used the extra command as officers and an extra standard bearer. This set also has swinefeathers for all the musketeers.
The Imperialist set is similar but has 4 extra metal armored pikemen, two held up in both hands and two carried on shoulder. The set contains 1 new officer, again with arm options, he is perfectly suitable for ECW. This set also has plenty of broad rimmed hats as extras and enough rests for all the musketeers. The extra hats are great, they give the troops a traditional 'puritanish' look if you follow me.
Both sets I think are ideal to add variety to an ECW army, and are in my opinion fantastic value, for just a few pounds more you are getting 5 metal miniatures (The command in particular are really beautifully sculpted minis), plus all the optional extras, I really like my pikemen to be helmeted so that is a plus for me, and if you are looking at an early war army or Trained Bands then you coud even give a few musketeers helmets and use all the rests.
I still need 2 more boxes of minis to finish my Parliamentarian foot and my royalist foot, and I shall buy these rather than the standard ECW ones because of all the extra options and the great value.
Hope this helps.
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