Microsoft’s augmented reality Hololens goggles are getting a rough ride in tests by the US Army, according to internal military evaluations seen by Bloomberg and Insider.

Soldiers testing the headsets have complained about their “mission-affecting physical impairments,” and say that wearing the goggles can cause headaches, nausea, and eyestrain. Acceptance of the tech “remains low,” says a summary prepared for Army and Defense Department officials and seen by Bloomberg, with soldiers complaining that the headsets don’t “contribute to their ability to complete their mission.”

One testimony reported by Insider was even blunter. “The devices would have gotten us killed,” said the tester — referring to the light emitted by the goggles’ head-up display, which could alert enemy troops to the wearer’s presence.

Although these reports highlight shortcomings with the tech, they also point to tangible improvements, such as the hardware’s reliability. A spokesperson for the Army told Insider that tests of the goggles — known as the Integrated Visual Augmentation System, or IVAS — were so far considered to be a success.

“The emerging results indicate that the program achieved success in most of the Army evaluation criteria,” Brigadier General Christopher D. Schneider told Insider in a press statement. “However, the results also identified areas where IVAS fell short and needs additional improvements, which the Army will address.”

Microsoft won a series of contracts potentially worth tens of billions of dollars to supply the US Army with its AR glasses. The contracts have been seen as validation not only of Microsoft’s augmented reality strategy, but of the feasibility of the AR tech in general. The goggles are intended to provide soldiers with live information on navigation and commands via a head-up display, as well as offer thermal and night-vision views.

Earlier this year, a Senate committee cut $350 million of the Army’s $400 million procurement request to buy more units from Microsoft, stating that members were “concerned that IVAS continues to face software, hardware and user-acceptance challenges that the Army has not sufficiently addressed.” However, the Army is still pushing ahead with the project, and started taking delivery of a first batch of 5,000 goggles in September this year.