I've been using the malectrics tab welder version 2 for the past 2 years and it never let me down. I only use 0.15 nickel strip, it easily does that with power to spare. The version 2 is primitive with just one LED to show the power setting, the newer version is a major improvement with a nicer status screen, but I'm still happy with version 2. To me price is a big factor, the malectrics is about 90 dollars.
I've seen the kweld in action and it looks excellent and it does 0.3 nickel strip with ease, but I don't see myself spending more then 100 dollars to get better performance that I don't need or will ever use. I notice in the kweld they use 8 gauge probe cables and still got excellent performance. Also the kweld can use capacitors to power it, something malectrics doesn't do.
Here is a picture of the malectrics, instead of a foot pedal, I just use a momentary switch and placed it by the probe tips. The probe cables are 6 gauge pure copper welding cables, and the probe tips are copper nails. Which ever welder you get, definitely get 6 gauge pure copper cables, they make a major improvement in keeping the cables cool and delivering good tabs at lower power settings. I use xt90 connectors to connect to my 27ah agm battery. Notice the custom case for the welder.
I was using 8 gauge copper clad wire before and after 15 cells, the cables were too hot to hold. I had to let them cool down for 10 minutes and it was taking along time to do a project.
How I look at it, the malectrics is for the hobbyist who builds an occasional pack every once in a while, the kweld is for someone who demands the best and will actually use its full potential.