The Mitchell reel is a phenomenum. Over 10 million 'egg shaped' reels were made in Cluzes up in the Alpine region of the Haute-Savoi. The reel was designed around the spool. No other reel had such a depth of spool which made casting further much easier. The design of the oscillation was the key to its sucess. Normally the depth of spool was restricted by the diameter of the main gear. Mitchell doubled that. However, they made it with the rotor turning the 'wrong way' for the majority of anglers. That probably cost them a few million extra sales, particularly in Britain.
Mitchells success stimulated other local companies to try their luck making fishing reels. One of them, SAP produced a reel using worm drive rather than the large gear driving a smaller pinion.
British companies couldn't use worm drive as Hardy held the British patent. But reel makers in France, Italy and Germany weren't subject to the restrictions. The manufacturing cost of worm drive caused the Italian Alcedo company to go bust. DAM however made worm drive reels for many years. Another Cluzes company were Bretton. They outlasted Mitchell without ever achieving anything near the same success. Bretton reels were the last fixed spool reels to be made in Europe.
Hardy used worm drive for their Altex reels and allowed Youngs to use a worm drive gear in their Ambidex models. The gear however was made from Tufnol not steel. ABU were served notice that their fixed spool reels manufacture was to be re-located to Asia. Before that happened their engineers designed and made the Suveran models using worm drive gears made from non-magnetic chrome steel. The very expensive stuff Rolex watches are made from. It was a two-fingered gesture to the new owners of their company.
Ultimately Mitchell were taken over by their US distributors and their bean counters ruined the company. Just like happened with ABU.