Bkr bottles are made of glass - but not glass that can withstand extremes of temperature - so filling them with boiling and really cold water probably isn't a good idea! They have a silicone sleeve that can be removed. What drew me to these bottles was the fact they were reusable, they're pretty and the fact that they aren't plastic. I only drink water when at uni (plus or minus the odd cup of green/peppermint tea) so a reusable bottle is a must. In the past, I've used plastic Evian or Highland Spring bottles but I wanted something a bit more permanent.
I dare you to say that they aren't pretty? The silicon sleeves come in different colours and I've even had someone say that it is the 'best looking water bottle they've ever seen'. For me personally, I think it is designed perfectly. The opening is wide enough for you to take a decent volume of water per sip whilst ensuring minimal leakage and that it is still easy to refill at a water cooler/fountain.
Portability and Durability
Being glass, it is going to be heavier than any plastic alternative but the cap makes holding the bottle pretty easy. The silicon sleeve also gives it a fair amount of protection and I've yet to have one break or chip (touch wood this continues!).
Ease of Washing
Getting the silicon sleeve off is a bit of a mystery at first but the makers of the Bkr bottle have helpfully uploaded a Youtube video about how to remove them. All components are easy to wash and I wash them at least twice a week.
Before I bought a Bkr, I honestly didn't believe water could taste different depending on the type of drinking vessel used but I definitely believe it now. The difference is subtle but water from a glass bottle tastes fresher and less artificial.
In conclusion, I don't regret shelling out for these Bkr bottles. They have enabled me to up the amount of water I drink on placement whilst also looking pretty cute! They might be a bit of a pain to lug around due to their weight but to me, it's worth it. I just wish they would sell the sleeves separately.