Mark is generally agreed to have been written before Matthew and Luke, the latter two having used Mark as a source. However, Matthew and Luke evidently had a different (and probably common) source for the temptation narrative. This hypothetical source is referred to by scholars as Q. It is clear that the agent of temptation in the Q source was ho diabolos (the devil). Matthew and Luke reflect a separate, more detailed temptation tradition which does not seem to be dependent on Mark. Neither Matthew nor Luke include's Mark's detail that "he was with the wild animals", and both Matthew and Luke use ho diabolos as the main designation for the tempter as opposed to Mark's ho satanas. Of course, ho diabolos and ho satanas are equivalent and interchangeable terms, as is clear from Matthew 4:10 and other passages such as Job 1:6 (Hebrew and LXX), Mark 4:15/Luke 8:12, and Revelation 12:9.
Thus, Mark shows that there are two independent and early strands of tradition which attribute Jesus' temptations to Satan/the devil. It is thus very likely that this attribution goes back to the teachings of Jesus himself rather than being the literary stroke of a later writer. (Of course, Jesus must have recounted the wilderness temptation to his disciples, or otherwise we cannot explain how the tradition came about, since no eyewitnesses appear to have been present.)
The other significant feature of Mark's version of the temptations is its very brevity. It is evident that Mark regarded the sentence, "And he was in the wilderness forty days, being tempted by Satan" as self-explanatory. Mark was able to assume that his readers would understand what he meant without providing any further clues as to the identity of this 'Satan'. This is remarkable since satanas is not a Greek word but a transliterated Semitic term. Mark often uses Semitic terms in his Gospel but usually provides a translation for his predominantly Gentile readers. In this case, he provides no translation or explanation. This suggests that Mark regarded ho satanas as a proper name or, at the least, as a specific theological term well known to his readers.
Thus, we need to ask ourselves, at the time Mark wrote his Gospel (c. 50s or 60s AD), what concept of ho satanas could have been well established in the church? The most likely answer is a concept of 'satan' found in the Old Testament and/or intertestamental Judaism. The problem is, while 'satan' is used for personal beings (and in some cases, arguably a specific personal being) in the Old Testament and intertestamental Judaism, there seems to be no evidence for a well-developed figurative concept of 'satan' at this time. Mark thus presents the Christadelphian view with a real historical difficulty.
The question is, in a mid first century context what did ho satanas or ho diabolos (without qualification) refer to? Ultimately we should make recourse to Job 1-2; the writings of Second Temple Judaism also provide useful background. However, right in the Gospels we have an account of a dispute between Jesus and his contemporaries about a personal ruler of demons whom Jesus refers to as ho satanas. Now, it has been claimed that Jesus merely assumed this view of Satan for the sake of argument (though I've argued elsewhere why this interpretation doesn't stand up to scrutiny). However, what is more immediately relevant is that the dispute establishes that 'the satan' was in contemporary Jewish usage the title or name of a specific personal being. This also forms an important part of the larger Gospel context against which 'THE satan' and 'THE devil' must be understood.
Thus the use of the definite article in the temptation narratives shows that a particular being or figure is in view. This rules out any possibility of interpreting the tempter as an unspecified human opponent. Moreover, in light of the Beelzebul controversy we have grounds for claiming that Jesus' contemporaries would have understood ho satanas to be the designation of a specific supernatural being. The Christadelphian view faces a serious obstacle in the lack of evidence for a figurative concept of 'satan' that had become so entrenched in the church by the time the Gospels were written that the writers perceived no risk of misunderstanding in describing Jesus' tempter as the devil and the satan without qualification.
Furthermore, it should be noted that the statement that angels came to Jesus (corroborated in Mark 1:13) establishes beyond any doubt that Jesus did interact with supernatural personal beings while in the wilderness.
However, what we do not find are dialogues between personified figures in which one speaks and the other answers, back and forth. And we certainly do not find such dialogues between a literary device and a literal person! To claim that this is what is happening in Matthew 4 and Luke 4 is to require the writers to have invented a brand new genre -- and camouflaged it within a genre which is normally read in a straightforward, literal manner!