Normcore are one of the most well known brands of home barista gear, and their spring loaded tampers are among the better regarded, medium priced calibrated tampers.
There are some astronomically priced tampers, and the tamper is very important, but what's important is being able to achieve a consistent tamp and a level surface. The Normcore spring tampers not only achieve this at a fairly reasonable price point, but they're of a very nice build quality, they're made using premium materials, and they come with adjustable springs.
Features and Benefits:• Spring loaded, calibrated tamper with three springs, 15,25,30lb
• Black Aluminium handle
• Flat, stainless steel base
• Ensures consistent tamp force & level puck surface
So this is the Normcore V4, the latest version, and this is the version with the uncoated flat stainless steel base, and it's available to suit a range of portafilter sizes all the way up to 58mm.
If you're unsure about the bases, as long as they're flat, personally I don't think the base choice makes much of a difference. Data from people who have tested this would appear to show that curved base tampers hinder consistency slightly, so flat would appear to be best, and completely flat vs rippled actually seems to be slightly more consistent, although from what I can gather we're really splitting hairs.
The rippled base tampers leave a pretty pattern on the puck, it looks cool, other than that, there's no obvious benefit. In practice, I find that rippled tampers sometimes retain just a slight amount of coffee inside the grooves of the ripples, and this is possibly to thank for the very slight reduction in consistency of extraction in the tests.
In a nutshell, I'd just go for whichever one you like the look of, it won't make a big difference, and if you have no preference either way, I'd go flat vs rippled, personally.
What I think is particularly good about the Normcore tampers is the self leveler ring and the adjustable springs.
The self leveling ring connects with the rim of the basket, so as long as you ensure that this is kept flat, you know you're getting a completely level tamp, which is surprisingly difficult to do without a levelling ring.
The adjustable springs allows you to go from between 15 - 30 lb of pressure, and in my humble opinion, the 25lb spring is the most sensible one to use.
I believe 25lb of force, about 11Kg, will sufficiently tamp the puck, and although the additional 5lb of force from using the stronger spring probably won't do any damage to the shot, over time tamping with more force than is absolutely necessary could put unnecessary stress on your joints, while probably giving you little or no improvements in shot quality to show for it.
If, like me, you're falling apart ;-), and you have dodgy wrists, I'd recommend trying the weakest spring and just seeing if you get on OK with it. In theory just under 7KG of force is a bit on the small side, but some people swear by not tamping at all, just using a distribution wedge, and appear to get results that are satisfactory to them. If you try the 15lb spring and you're happy with the results, then great.