Firstly do you have heart issues, battery operated medical implants, pregnant (there are other contraindications) but these are the main ones, because if you do its not recommended to use violet wands and I think Tens too, but you need to check on that, as violet wands is my jam.
Not everyone likes the feel of solid state violet wands. They tend to feel very prickly in a very sharp way, whereas mechanical violet wands be they modern or vintage restored feel different. Its sort of like the difference in sound quality between analogue and digital recorded and reproduced music. Its thought its the frequency of the electricity, on an oscilloscope the mechanical might look more like a wave and the solid state more like a series of squares. I am trying to create an image here, rather than how an accurate measurement would look, artistic license.
There are only two main choices in this (I will not be mentioning wanda here, best avoided)
Modern Solid State. Most of these are made in China, a handful in Ukraine, and are sold for the beauty market. These are referred to as derma high frequency devices, they are usually low powered and will come with 4 or 5 glass violet coloured electrodes, or neon coloured electrodes. In the old days (1920s and later) some claims were made that different colours have different healing properties, but that is tosh in my view.
These Chinese sourced high frequency devices are pretty cheap and will give a bit of a taste, but the low power for many isn't enough. There is away around this, and that is buying non glass electrodes from a gentleman based in Costa Rica. He designed these to give more perceived effect/power from a low powered device. They work brilliantly, and there is plenty of choice of non glass electrodes from him, including a few internal ones. A safety note here, never ever, ever use glass electrodes internally. It does not matter a jot what these glass electrodes were originally designed for, please avoid potential life changing injury and a visit to hospital just don't do it.
There is one guy out there who has a Chinese made derma wand tweaked to have more power, and it will be better than straight from China devices, or from Ukraine (best avoided non standard electrode size) as it has a bit more output power and its noticable. Combine these with those non glass electrodes and yum yum nastyyyyyyyy.
Next option is mechanical and most kinksters into violet wands opt for the only modern one , the BD10, which comes in standard or A version, with a deadmans switch on the top. It must be held down to work and this gets tiring, but you can gets hands free hold down via a velcro strap. These have a lot more output power, at least another 20/25% more than the Chinese sourced devices.
Solid state make little noise, a slight hum, but a BD10 in use, has a loud mechanical vibrating typed noise, this is the internal vibrating hammer that helps create the output power, as you turn it up it vibrates more. These are repurposed vintage medical devices, violet ray machines, no longer used on humans but for leak testing a roof or neon lights, also common in many school science labs, along with Van de Graaff generators. These use a tweaked version of tech designed by Nichola Tesla, and refined by Oudin. The supplier of BD10s also has other more expensive options, but then you are stepping into restored vintage machine prices.
The big problem with the BD10 option is no electrodes supplied with it, and the hot shot it is supplied with, is not suitable for casual play, its for leak testing and is very severe in use outside this function, though hard core pain junkies might well love it. I would also not recommend using the non glass electrodes with it, I think the overall effect is way too intense. Fine with solid state, but match them up with mechanical and its going to be way too much for most people.
Now it is possible to buy some of these items as a kit, with extra bits and pieces, such as light bulb holder (light bulbs are fun to use, working or not, though ones glowing green best avoided, that green glow is xrays..... gulp) a body contact cable, some conductive items etc to increase the degree of play options.
This is already a long reply, if you would like more explanations and options have a read of my blog on the topic.
https://thecage.co/blog/userblog.php?blog_id=15139&postid=28393
I haven't mentioned vintage restored because no kink friendly restorers in USA, only one alternative healer type, and the vintage US devices available are not that great, and the superior European ones are now so expensive as to be not worth it, in my opinion.
Hope the above is helpful.