Labour to fit either will be the same. If fitting springs, fit good quality ones.
Another well regarded brand to consider is California’s Racing Beat. Racing Beat are basically the people behind Mazdaspeed products since about 2004, and naturally have a close relationship with Mazda
Interesting that their NB1 springs are a bit different from NB2.
Also Tein
https://uk.tein.com/srch/uk_search.php?maker=MAZDA&carmodel=MX-5&modelyear=1999-2005&item=default&genuine=0&tuvchk=0
What’s important to thnk about is the rear spring bias (spring rate ratio); how stiff the rear springs are in comparison to the fronts.
Different springs were fitted to various NBs.
Front/Rear:
Stock NB: 162/118 lb per inch
Tein S Tech: 235 / 173
Eibach Pro Kit: 228/137
Racing Beat: 195/145
So, you will notice a very different ration with the German Eibach compared to the Japanese Tein. Tein keeps closer to the factory split.
Someone with a great deal more knowledge than me on MX5 suspension said:
“Grip varies inversely with roll stiffness. Thus, if you stiffen one end’s springs or swaybar, it will lose grip and slide at lower loads than previously. E.g., stiffen the front to get more understeer (or less oversteer)”
So softening the rear spring decreases oversteer(more grip at the rear) but increases understeer. The Japanese like a looser rear end for more “sporty handling” in gymkhanas.
Spring rate can be misleading. It depends on the shock. A good shock can have apparently very stiff springs, but the ride quality can be fantastic (eg. P5 Puredrives). Standard shocks might be overpowered by stiff springs, and the ride can end up choppy.
If you are not fitting yourself, I would seriously consider at the same time also replacing the shocks, or at least renewing things like the bumpstops. The lower featured “name brand” shock-springs sets (Gaz, Koni, Tein) will be better than the Chinese (PRC or Taiwanese) sets, which are generally built around a generic tube (this is why they have gone for these “extandable shock bodies”; its a way to use the same shock on many different models, with easy changes). At the really cheap end you have the Raceland/Rokker coilovers (adjustable for height, fixed shock body). The shock body, when cut open, turned out to be containing a shock insert stuffed in a threaded tube, probably for something like a Micra. I’m not sure i fthis is basically what the Vmaxx shocks are.