I adore this cup - a great size for a decent amount of drink. My Americano coffee stays beautifully hot for 90 minutes - perfect when doing a long journey.
I have been so pleased with the size and functionality of my cup I have bought 4 of them as gifts.
The leak proof functionality is great. When picking up the latest one in Poole I said to the John Lewis partner that if you are asked for advice this is the one to offer. I dont know why all reviews are not as glowing as mine

I gave this mug 3 chances! The third time I actually preheated the coffee in the microwave to ensure that it was boiling when I poured it into the mug. I also filled the mug with boiling water immediately before using.
Still the drink was barely warm enough when I came to drink it less than 2 hours later.
In conclusion, probably fine for keeping coffee warm by your desk for about an hour, but unsuitable for use outdoors after a walk.
On the plus side, J Lewis exchanged without any problem

I have purchased both the 250ml and the 350ml Aladdin travel mugs from Lakeland. They look good, are most convenient sizes, and the leak proof flip-top lids are fantastic. I particularly like that the lids are interchangeable between the two sizes, so there's no wondering which lid fits which mug. When going out I can, say, take cold water in my white container, and coffee in the other. I hope Lakeland repeat this review for both the Aladdin 250 and 350ml items because they both deserve top marks.

Didn't know I could get enthusiastic about a pot to keep my brew in. This Aladdin thermo mug is that good! It is the perfect size for tea or coffee, has a grippy external wrap over the aluminum double-layer thermo pot so it doesn't easily slip from your hand. The lid closes and locks very positively and the mug is leak-proof.
One tiny thing: I wish it had a loop to put a finger through when I'm carrying the mug from the kitchen with other 'stuff' back up to my office - small point but would be a great addition.