One reason why I prefer the series is that it is not necessary to implement the series aspect of a series until one is ready. So until you create a cell in a series, the company operates exactly the same as a traditional LLC. Thus, providing the investor the option to deploy the series element of the series when they so choose. If the individual forming the LLC were not to include this language in the initial filling but wanted to form a series later, this would require another filing with the secretary of state to amendment the certificate of formation.
While Texas LLCs are relatively inexpensive to file, and have no annual fee (besides possible franchise tax costs) your CPA will likely charge you separately for each return that needs to be done. Additionally, if you form your company the right way (having a professional help you) each LLC will cost more than $300.00 to form whether it is a series or traditional LLC. I believe that the "risks" that have been pointed out are in regard to the fact that the series LLC has not been heavily litigated by our courts. While this is true the statue clearly describes how to form and operate a series to maintain the division of liability amongst each cell just as is laid out for traditional LLCs. See below.
Sec. 101.602. ENFORCEABILITY OF OBLIGATIONS AND EXPENSES OF SERIES AGAINST ASSETS. (a) Notwithstanding any other provision of this chapter or any other law, but subject to Subsection (b) and any other provision of this subchapter:(1) the debts, liabilities, obligations, and expenses incurred, contracted for, or otherwise existing with respect to a particular series shall be enforceable against the assets of that series only, and shall not be enforceable against the assets of the limited liability company generally or any other series;(2) none of the debts, liabilities, obligations, and expenses incurred, contracted for, or otherwise existing with respect to the limited liability company generally or any other series shall be enforceable against the assets of a particular series.
Note that for the above to be true there are certainly formalities that must be maintained as well specific language that must be included in formation and company documents.
Disclaimer*I am an attorney, but this is not legal advice, just friendly information. You definitely want a professional to look at your particular circumstance and help you come to the right structure.