Undoubtedly, digital investment advice platforms have gained a solid foothold on Wall Street.

According to Cerulli Associates, robo-advisor platforms have accumulated more than $71 billion in assets under management through the third quarter of 2016. That number is expected to grow to $489 billion by 2020, or about 22% of all assets managed by registered investment advisors. Mostly, those platforms operate under the banners of major investment brands, like Fidelity Investments and Vanguard Group.

Investors seem drawn to digital investment advisory platforms because of lower fees relative to flesh and blood managers. According to Cerulli, the average robotics money management fee ranges between zero and 0.89%.

But a recent report from Martinsville, N.J.-based Condor Capital Management throws some serious shade on robo-investment advisory programs, claiming that portfolio results vary "greatly" from firm to firm.

Condor's report, under the stewardship of company president Ken Schapiro, opened investment accounts at over a dozen robo-advisory firms.

Using a standard investment portfolio of 60% stocks and 40% bonds, and a retirement time table of 20 to 30 years, Schapiro offered the same investor risk profile to each firm, and placed his accounts in a higher tax bracket.

One year later (at the end of 2016), Schapiro says his portfolio returns at eight firms varied from 5.55% at Vanguard and 10.75% from Charles Schwab.

"Given the comparatively recent emergence of these algorithm- and automated-backed products, we think it is important to understand what their characteristics are and how they compare because we believe in transparency for investors," Schapiro told The Wall Street Journal.

For its part, Vanguard cited erratic asset management performance in rejecting Condor's report conclusions, and also warned against the dangers of making too much if short-term returns. And Wealthfront, another robo-advisor, closed Schapiro's account down altogether, citing a "fatally flawed" study model.

But the report has succeeded opening a debate on the effectiveness of robo investment advisory platforms, which remain relatively new on the money management landscape.

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"Each platform and programmer has their own way to interpret data," notes Richard Reyes, a financial planner and founder of the Financial Quarterback, in Orlando, Fla. "In addition, computers can't think or know if the data you are inputting is realistic or true."

Reyes says he has yet to see an investor who understands all their investments, Social Security issues, pension, taxes, and their key risks in retirement and investing, and that hobbles any attempt to obtain uniform results under any investment portfolio model. "It's garbage in and garbage out - I have yet to meet anyone who can interpret and implement the results," he says.

Thus, robo-advisor services only really serves a rather small segment of the investing public, he adds. "Yes, they're easy, but robo-platforms still leave you vulnerable," Reyes says. "In total, it's your emotions that control your results, and it's your (portfolio) inputs that control your results. There is no one to guide you but a machine that has no feeling, concerns, desires, or any idea who the heck you are and what you are trying to do."

Machines don't have quite the backstop real life financial advisors do, Reyes says: "So when you do something stupid or panic there is no person on the other end that tells you, 'You're doing something really stupid, so stop doing that.'"

Also, just like human-based investment models, different digital investment platforms have different structures, algorithms and styles.

"While the name 'robo-advisors' might suggest a strictly automated investment process, there is still a strong human element involved and thus a wide variability in risk tolerance mythology, trading protocol, fund selection, and fees," notes Stoyan Panayotov, founder and wealth advisor at Babylon Wealth Management.

For example, one of the most important factors for superior portfolio performance is asset allocation and how it's assigned based on risk tolerance, Panayotov explains. "Various robo advisors differ widely in their methodology of assigning a target asset allocation based on a set of questions," he says.

"First, a client can be assigned to a different risk tolerance category depending on the advisor's questionnaire," he says. "Second, even if the client is assigned identically to the same risk tolerance group, there is no guarantee that the robo advisor will offer the same exact asset allocation. Third, even if the asset allocation is the same there could be wide variations in terms fund selection, trade execution, expense ratios, tax loss harvesting mythology and management fees."

At the end of the day, Panayotov states, "it comes down to the quality of execution of various factors that come into play in measuring portfolio return."

Expect the growing debate on robo-advisory platform portfolio results to heat up. With about $37 trillion in total investable assets under management on the table, the stakes are too high for Wall Street firms to cede any ground, be it to robo-advisors or human ones.

As for real-life investors, the watchwords are caution, due diligence, and focus. All three attributes will surely come into play with different investment portfolios, no matter who's managing your money.