Is Taxpros19 a legitimate source to obtain a TurboTax Deluxe download?

very unlikely.  Be back in 3 minutes after I do a check on their domain.

In the past month, a number of individuals posting complaints about the failure to execute properly, failure apparently to connect to a network and other strange activities of the software they have downloaded and installed have all been traced to purchasing purported TurboTax software at deeply discounted prices from entities that only have a web appearance without any proper address or means of contact.  These entities at best are a filing with an internet provider where they host their webpages, and the actual entities, many of them, have been traced to foreign countries.  

The same criminal entities have been posting under a large number of domain names.  The common aspects have been a domain name with "tax" and a deeply discounted price.

It would not be surprising if one were to find out that the individuals who have purchased this fraudulent software will find their personal financial information from whatever they have entered has since been stolen and circulates the world of stolen identities.

Keep your purchases to known identities such as TurboTax, Amazon, Walmart, Staples - and do be aware that early in January, both Costco and BJ's and possibly others, have a week or two of coupons resulting in legitimate deep discounting of price of TurboTax.

No. they've already been reported.  Although Turbotax does not publish an official list, authorized retailers will be names you know, like Amazon, Staples, Best Buy, Costco, Target, Walmart, etc.  Any online site that only sells tax software is almost certainly a pirate site.  If you are lucky, you only get an unauthorized copy.  If you are unlucky, you could get scammed out of your money, get a damaged or crippled version, or a program infected with viruses and malware, and the web site may sell your credit card number on the black market.  

This particular site was registered with GoDaddy on November 6 and their contact info is anonymous.  Do you think real businesses use Go Daddy?

not only possible malware, but consider that you will have to provide them with your credit card info and probably e-mail address.  just think of what you'll have to go through if that info is posted on the dark web.