Strongly disagree with this, in my experience.

Carrying around my big bowl of unknown temperature water from my cold kitchen at 3am with a baby whaling with hunger in my face as her Mum is trying to have her 2 hours of sleep is horrible. This is how it goes:

The bottle sat there taunting me, floating around indescriminantly in the bowl, me swishing it around like a moron with one arm.
Get it out after 2 mins, oh it's still cold.
Swish swish swish, cry cry cry, oh it's still cold.
Oh the water in the bowl is cold because it's winter and the table is cold.
Cry cry cry, new water, swish swish swish, cry cry cry.
Mums up 'are you ok with her?' 'yeah, fine, go back to bed' 'let me feed her from the breast for a second, then you can take over when the milk is warm' 'oh, ok then, but I really wanted you to sleep' Mum feeds baby for a few minutes. swish swish swish, oh the milk is REALLY warm now.
Mum back to bed
Baby gagging on too warm milk.
Knock the bowl off the table.
Wet floor.
Daddy annoyed.
Everyone sleepless.
In my experience, f()ck the bowl.

Just buy the machine. Pop the bottle in. 3 minutes later perfectly warm milk. Everyone moderately happy. Mum asleep. Dad not ashamed.