Are engineering TECHNOLOGY degrees actually useful?

An ET degree is not nearly as rigorous as an engineering degree. There will certainly be jobs, but these will be technician jobs. Unfortunately, most US tech jobs are 2 years degrees (A.S.) So you friend will possibly have spent 2 additional years in college only to do the work of someone with an A.S.

Also, ET's cannot take the PE exam (at least that was true several years ago).

An engineering B.S. offers more growth opportunity and higher wages, if he can handle the coursework.

Engineering technologists are graduates of bachelor-level programs in engineering technology. They apply engineering and scientific knowledge combined with technical skills to support engineering activities. Their areas of interest and education are typically application oriented, while being somewhat less theoretical and mathematically oriented than their engineering counterparts. They typically concentrate their activities on the applied design, using current engineering practice. Technologists play key roles on the engineering team; they are typically involved in product development, manufacturing, product assurance, sales, and program management. TAC/ABET specifies that faculty who teach in these programs have a minimum of a master's degree in engineering or engineering technology or equivalent, or a PE license and a master's degree.

Sure, my friend completed his DEC in engineering technologies in college and is pursuing mechanical engineering in university. Engineering technology programs are more than suitable for people if they feel they're capable of being on the job.

Yes, they tend to be more focused on "practical" considerations and less on high level (detailed) engineering theory.