I haven't worked with MVentix, though I have been signed up with them for quite some time. If you are working through their website, they are definitely a legitimate company.
I have no issue with providing my bank routing number (9 digit) and account number as well as identification whether it is a checking or a savings account. I will, however, only provide it through a secure website (watch in the URL bar at the top that it says https:// If it just says http:// it is not a secure site). Certainly my preferred form of payment is via direct deposit because there is no nonsense about checks, "Lost in the mail." While PayPal is fine, I do like direct deposit better because there is no clearing time to get the money from PayPal to my bank.
As for social security number. While technically I believe companies can wait until you approach the $600 mark where they would need to send you a 1099 to get the number, in reality these guys need to cover themselves that they are not 'hiring illegal aliens' and they need to tie payments up to a social security number in case of IRS audit. They also use the social security number to make certain that if they terminate me as a shopper for cause, I don't just bounce back at them with a new identity. Since every dollar I earn must be accounted for with IRS anyway, whether they 1099 me or not, I may as well provide my number. Again I look for the https:// in the URL bar.
The other personal information a company asks for generally is demographics. My age, gender, size, annual income and education may disqualify me from some work while qualifying me for other work. These kinds of questions are routinely asked and my only regret is that all too often schedulers don't use the information they have been provided in my profile to send me offers for work in my area that I am qualified to do. I am very tired of the excuses they have used for what appears to be pure laziness when I have questioned shops at locations 3000 miles away, for someone 40 years younger. (You might be going to Alaska or know somebody who lives there!)
Companies may also ask with what banks you have accounts, what credit cards you may have, etc. These tend to be client specific questions. If I have a checking account at ABC Bank, then I am already set up to do teller shops and possibly platform shops with ABC Bank. One company recently asked me to purchase my credit score (they reimbursed) and send it along. Not the first time I have done this for this company and I recognize the need for it in that they seemed to be sending high scoring and low scoring 'customers' through a shop experience evidently to see if/how they were treated differently. It was a request from a company I have very high regard for, so I did not question at all their request.
Over time you will build trusting relationships (and distrusting ones) with various companies, but they all need your most basic demographics. While in several cases databases have been compromised, it is overall rare. My data has been compromised twice that I know of in the past 5 years and there have been no repercussions. Most companies that have secured sites also seem to have reasonable encryption of their databases.