I have owned 10 .375H&H rifles.3 Browning Safari grades, a Sako AIV Safari, a Sako AIII Deluxe, a Winchester Express CRF, 3 CZ 550 Mag Americans, and a custom BRNO 602. Today I have only one, a 1960 Belgian Browning with a European walnut stock, claw extractor and all steel bottom metal.
The Whitworth is based on the Yugoslavian made commercial M98, same as the Mark X from Interarms.
Functional but crude though considerably better than today's Zastava. The post 64 controlled round Winchester mod.70 with MOA trigger, made in USA (Now made in Portugal) had excellent rear sight(ERA)
and was very slick. The action is designed to accept the .375 without removing metal that supports the lower locking lug also the lower lug is not slotted for the ejector. This makes the action stronger than the FN 98 for 3.6" cartridges. The CZ 550 is OK I guess since it is used by PHs all over Africa.
The thin magazine box and soft follower take a beating even after relatively few rounds.This is also true of the Sako. If you plan to feed rounds directly into the chamber to sight in a scope remove the follower from the magazine. When the follower has little pressure on it it will smack into the front of the thin stamped steel mag box and deform it. My CZ mag box bent so much that the cartridge tips would catch on the loading ramp.
My 2 cents is that the Winchester Mod 70 Express is the best out of the box for the money.