I have the opportunity of scoring a free 2.5 x 2.5 m polytunnel from a mate.

What experiences have you folk had with polytunnels/glasshouses?

What benefits do you see, what advantages and disadvantages.

FYI if needed we have frosts in winter sometimes down to -2, summers in to
the mid 20s and sometimes high 20s with humidity and decent rainfall through
the year. The polytunnels will be unheated if used.

thanks
rob