I have two TIG machines, a Miller Goldstar and a Lincoln 200. The Goldstar I have is a special machine in that it has 4 ranges instead of three. The 4th range is from 1 to 10 amps. I used this very low range for welding stainless foil. The Goldstar also is just a sine wave machine when using g AC.
The Lincoln is only a 200 Amp machine whereas the old Miller Goldstar is 300 Amp machine. So I am keeping the old machine just in case. Anyway, the Lincoln is indeed an inverter machine. It weighs about 70 pounds. The Miller weighs about 700 pounds yet only has 33 percent more power. The Lincoln is an excellent machine and I was amazed how easy aluminum welding was with the Lincoln compared to the Miller.
You can buy welders that have more options, and are more versatile, than the Lincoln, for less money. But they will be made in China. When I bought my Lincoln I also looked at Chinese machines, and almost bought an Everlast. But the reviews weren't that good for the Chinese machines but the Lincoln had much better reviews and my purchase was for my business and I needed reliability and quick service.
Now I would probably buy the Everlast because they seem to have ironed out the reliability problem and apparently the quick service issue too. Though I have no direct experience.
All the new welders, except maybe some stick welders, are inverters machines. This is actually good for several reasons. The main reason being that inverter technology is mature and well understood. Every computer made since at least 1985, and maybe before, has an inverter power supply. This technology has blossomed and is used almost everywhere voltages need to be transformed to any significant degree.
Inverters are so popular because they are efficient and versatile. The efficiency comes in a large part from lower energy losses by using higher AC frequencies which leads to lower losses in the inductors changing the voltages and because smaller inductors are used. The versatility comes from the fact that DC must be changed to AC for an inverter to work. In fact, that is why they are called inverters. But once DC is chopped into AC at a certain frequency why not change the frequency to whatever you want? And, unless you need a smooth sine wave, why not keep the square wave that inverters naturally produce? Then, because you can switch the AC at whatever frequency you want, it makes sense to switch it at the best frequency for the job. And even the duty cycle of the square wave can be chosen easily. So much time at positive and then so much time at negative.
The description above does not cover all the advantages and versatility and waveforms of modern inverter power supplies, but does give a general outline of why virtually all modern welders are inverter power supply machines.
Finally, do I think it is worthwhile to change to a newer "high tech" inverter machine? If you are welding much aluminum then yes, it is definitely worthwhile.
Eric