No don't do it. Use the money to pay for an actual qualified therapist who is BACP qualified (don't get someone from one of the dodgy self-regulating self-defined acronyms that isn't a real governing body with proper entry requirements and training expectations of therapists).
The "mental health" industry is now a billion dollar industry with so many fakes, frauds, charlatans and snake oil salespeople. If these sort of things actually worked, don't you think there would be scientific studies and it would be all over the national news not just a puff piece in the occasional lifestyle mag?
Review manipulation is a real issue at the best of times but with expensive products, they can do all sorts to encourage positive reviews because so much money is at stake if they pull it off. You have selection bias that the people writing the reviews have been prompted by Amazon and people who are still depressed are likely to feel apathetic and less motivated. You have bias that Trustpilot is very hot on taking down people's genuine reviews if companies complain to them enough.
You have bias that some people will have received a free sample or heavily discounted in exchange for a review, and these people will not have necessarily have been anxious/depressed in the first place, but they will report all sorts because they got a free expensive product that they can resell on eBay or elsewhere once they've upheld their end of the bargain by writing a glowing review. You have bias that people want it to work because they've just spent a huge amount of money on something in sheer desperation that it might work.
What people are actually doing is giving themself a mild electrical shock which makes them think something is happening. This device is just a mass-produced transcranial current stimulation device and we've known for years the evidence doesn't really support their use.
Even NICE has stated this should only be used by a qualified professional and that they must report this use to their clinical governance leads. Here are their list of side-effects, including risk of mania/hypomania which is a significant potential side effect for anything being done outside of clinical supervision: https://www.nice.org.uk/guidance/ipg530/chapter/5-Safety"
The NICE guidelines also state that the results are "inconsistent" and that a lot more clinical research would be needed before they could make any recommendations compared to the wide range of other treatments for depression/anxiety.
They are leaning heavily on the words "medically approved" which is actually a very dark grey area (almost illegal, in fact) under the ASA because it is misleading customers. This doesn't mean it's approved by doctors as a good treatment for mental illness. It means that the device has been tested as safe and hasn't caused any serious injuries so has been given permission to be imported/sold in the UK and EU and that the manufacturer claims it is a medical device. The MHRA don't check if the device does what it says it will do, they rely on the manufacturer's claims, the MHRA only ensure that it doesn't cause any significant harm. This is a direct quote from the ASA about what can/can't be said about "medical devices": "Because the onus is on the manufacturer to comply with the Regulations, manufacturers should not state or imply that their device has been “approved” or “certified” by the MHRA."
Real qualified psychiatrists have been playing with electricity around sufferers of mental illnesses for over 100 years. Read into the gruesome history if you want to horrify yourself with all the things they have done. Really, if there were any benefits to this at all beyond placebo, psychiatrists in hospitals would be queueing up to use these instead of having to book repeated slots in a theatre and with an anaesthetist (very expensive) to do a course of ECT on people with treatment resistant suicidality.
Please value your health and your mental health and get treatment from a qualified professional rather than spending a big sum of money on something like this. I say this as someone who has been stung by too many charlatans in the mental health sphere.