That is a great question. Here's the breakdown on this though.
Cisco is the only official provider material covered on the exam; everyone else isn't. So this includes MeasureUP, Transcender and even....Pearson Vue. All of them are competing for the same marketspace but no one has any advantage over the others as far as "closer" to the real exam.
Their competitive edge comes from SMEs (Subject Matter Experts) that can help them to word the questions better but because of the the NDAs (Non-Disclosure Agreements) that all certified professionals have to abide by or lose the possible certification they are all limited by what they can and cannot disclose.
The price difference also come in when you talk about the difference between a practice exam that's an application versus a list or an e-book of exam questions. Most companies pay a lot for the development and the polish they give to their exams. This is great but it comes as a cost to the consumer. So, I would pick any of those that I mentioned. I do recommend though that you stay away from so called "Brain-dumps." They may help you pass the exam but they didn't help you learn the knowledge you need in the field or on the exam.
Personally, I've never like the practice exam engines (applications) because I think it gives you a false sense of security. When I first took my CCNA back in the early 2000s, I used exam cram (red book, yellow bar across the top) and I read it astonished by how good it was to help me understand the why my answer was wrong versus why their answer was right. This helped me tremendously.
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