This episode is overall good and contains much of the goodness typifying the Pertwee Period of Dr Who...if you like Pertwee, Sarah Jane, Brig. Lethbridge-Stewart, Sgt. Benton, and the daffy cleverness of the vintage years for this show, you will likely enjoy this episode.
The standout feature for this chapter however, is an extended vehicular chase sequence which begins when a villain steals the Whomobile, and involves the Doctor's yellow Ford ('Bessie') and eventually involves a motorboat, a hovercraft, and an autogyro (some call it a gyroplane, but autogyro is a better term) similar to the Little Nellie flown by 007 in 'You Only Live Twice.' To anyone how has seen more than 3 episodes of this series, this episode is simply astounding due to budgetary reasons. For the crew to have gone on location long enough to shoot the required footage, to have fueled and operated the various vehicles shown in operation as well as the vehicles which had to become air and water borne to film the sequence, must have consumed more financial resources than were used in all of the 12 previous years of production. I tell you, it was a simply jaw-dropping experience for me.
Especially since, upon reflection, the sequence does almost nothing to advance the plot.
My best guess is that this sequence was created with the intent of impressing potential foreign broadcasters of this series, because in the 1970's, this series was eventually syndicated in various foreign markets, including USA. Car chases were HUGE in US TV during this era.
Whatever the reason, this is a very unusual episode, and for curiosity value alone it is worth viewing.