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.

If you liked this article you might like

Dividend Funds Need to Be in Your Life

Unlock the Secrets Behind Bitcoin Investing

Questions You Must Ask a Car Salesperson to Avoid Getting Ripped Off Big-Time

5 Surefire Ways to Destroy Your Marriage

Best States for Retirement in the U.S.