I would be gentle and careful in this kind of assessment. "Unorthodox" is a strong term. We have a tendency to overuse words and devalue their meaning.
Also remember many people in denominations or communions that hold to the dispensationalist framework do so nominally. It is sometimes not explicitly taught, perhaps assumed, but avoided as teaching topic.
Generally, even confirmed dispensationalist church members who know the system, know only a standard list of objections to "Calvinism." They do not know, have not considered the weaknesses of their own dispensationalist system, and they do not understand "Calvinism" at all. So, there is lots of room for engagement... way beyond just saying they are "unorthodox."
Before reading Mr. Gerstner's, Wrongly Dividing the Word of Truth, I would have said it was only a different interpretive system.
Now I would say it is an interpretive framework with huge weaknesses, and leads to major error.
Post Tenebras Lux; "And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever." - Revelation 11:15