We found most of the question types we needed were supported, but that was simply because most of the quizzes in QMP used a fraction of the question types available. We had some large sets, but we were manually importing questions and didn't have any significant issues. We were dealing with MCQs most of the time.
We use Blackboard quiz tool for low stakes summative assessment only, with no lockdown browser built in. Some modules may be assessed by a series of low stakes assessments which may add up to a considerable proportion of the marks for the module, but individually the assessments must all be low stakes if delivered in the Blackboard Quiz tool.
We run plagiarism awareness testing for all students new to the University in the Blackboard quiz tool, and it handles tens of thousands of attempts with thousands of enrolments on a single module. Be aware there are issues getting big attempt data like that out of the Blackboard GUI (Chrome for example, will choke on the gradecentre listing in a massive module (thousands of enrolments) because of insufficient DOM storage), but we are talking here about ALL new students in a given year (We use SQL in that case). No issues to speak of on a normal scale module with enrolments up into the hundreds.
University of Leeds