as long as he just has those two bottles and like you say sits down and has a cuddle and isnt walking around with a bottle permanently in his mouth or taking a bottle to bed with him then thats fine. just make sure you clean his teeth after the bedtime bottle :)
3 of mine bfed till much older than that and then ds4 was move to ff and he had a bottle of milk before bed until he was 3, the rest of the time he drank water from a cup and i just made sure to clean his teeth after the bottle :)
my dd is 17mths and has 2 bottles of formula, again just make sure i clean her teeth before bed (and in morning) and the rest of the time she drinks water but as you say its a nice comforting wind down time.
he may well gradually cut them down himself, ds4 did and then we reduced the quantity in his last bottle, until it was 4oz of so and then we went on holiday and 'forgot' it, offered him milk in a cup, his special buzz lightyear one but he was never interested.
with my dd i will just see how she goes, she only has 4-5oz in each bottle, one morning an done evening, will probably drop the morning one first and keep the bedtime one utnil she is older, and maybe do what we did with ds4, leave it behind or swap it for a special cup.