I don't think it is silly to get one for a baby of this age. I've no experience of this model, but have read some favourable online reviews. I think it should be large enough. If you google for video's of it, there was one on youtube by Kiddicare.com.
Hope someone else has more info for you.
Ps, i wouldn't be too concerned about speech in an 18m old just yet.

Its lovely to have them face you esp on long walks to school.. I find I do chat more to my lo when he;s in the buggy I can face towards me.
My 2.5 year old fits just fine and £55 sound reasonable!

Saw some good new ones on ebay for only 100 too. Also www.snunkie.co.uk had some lovely pics of one they'd made liners etc for.
I'm tempted myself, but i don't want to part with my Bj city elite!

Yes no problem, it's a nice big chunky pushchair. I think a 3yo would fit in in quite happily.

I think it depends what you term as "fits in" I hate their heads up near the hoods and unfortunately because of the way rear facers need to sit on the frame, the seats are never as roomy as a forward facer. I saw a child in a bugaboo yesterday and he was def younger than my DS (2 and a half) but he was chunkier and looked ridiculous! She had the hood hanging down the back (he was asleep) to give his head the freedom.....but he is only 18 months (yours I mean!!)....I have pictures somewhere of my son sat in the infitinity at a little bit older than that, but he is very petite and only weighs 26lbs even now. I'll have a look for you.

I know a lot of people on here liked them for the money though, I thought it felt really cheap and flimsy but I think it depends on what you have been used to?

FWIW, my son was rear facing for as long as he would comfortably fit but it didn't make a jot of difference to his speech! However, it is so nice to be able to chat to them properly without shouting over traffic etc or not knowing if they've heard you!

BabyG is 16 months old but a very big boy in 2-3 year clothes

We have an Infinity

School run takes an hour in total, twice a day, so we wanted parent facing. It's not an enormous seat but he fits in it ok, with room to move around.

Be very careful buying second hand though, I bought mine SH and the chassis was, to be blunt, absolutely knackered. The handle was held together by screws which I was informed was fine, but it wasn't really and the whole thing broke a few months after I got it

Luckily my mate's DC had outgrown their infinity so she gave it to me and I've managed to cobble together a decent pram using my wheels, her chassis, her seat unit and my covers!