Land's End is a big naff theme park. John O'Groats is little more than a cluster of souvenir shops and a hotel or two, plus another finger post photo stop. The nearest stations are each 20 or so miles away, at Thurso and Wick. But going by train with a bike in Scotland is a headache. Trains from Inverness to Edinburgh or Glasgow can only carry one bike at a time.
Couples have to split up.
Amazing but true. And you have to book in advance. If you don't, you could have an unplanned overnight stay on your hands. Apex fares are the cheapest bet, but you'll still spend well over 100 on trains. There's little point selecting a time to guarantee good weather.