I love the haakaa so much I bought 3. Invaluable. I had a cheap hand pump at the very start to deal with engorged breasts and I absolutely hated it. Made me feel ill using it. Thankfully using the pump for two days along with hand expressing in a warm shower, the engorgement and pain passed quickly. I binned the horrid thing and have used only haakaas since.
My routine is to have 3 clean sterilised haakaas on the bedside table each night (face down because they fall over so easily) before bed. During the night when baby wakes to feed I put a haakaa on the opposite breast while he feeds. Everyone is different but I have a lot of let down when feeding so that will fill the entire 100ml sometimes. Baby goes back to sleep and I freeze it immediately. I completely fill 2 or 3 haakaas each night. I have a solid supply of frozen milk that can be put in a bottle now for when my partner has the baby on his own.
In the early days (baby is 3 1/2 months now and milk supply has established and calmed down) I found the haakaa essential to use before I put baby on the breast. This was because my let down was too fast and he'd cry when feeding. Wee scone was getting absolute waterboarded! A couple of minutes with the haakaa to get the initial let down out meant that he had a nice slow and calm feed. Of course he cried for the couple of minutes while waiting! But it was better than the stress of him choking on a fast let down. I also got better at reading his hunger cues and learnt to feed him before the point of "hanger" (he takes after me 
)
Does the suction inadvertently increase your supply?
I cannot say I've noticed this. It's done nothing but help me establish my milk, keep my breasts from being painfully engorged, and provide a lovely supply of frozen milk.
How do you use these practically? After a feed do you feed it to baby straight away, put it in the fridge or freezer.
Don't feed to baby straight away. You need to be breastfeeding on demand to adjust your supply to your babies need. Once your milk is established, and you'll feel when you're ready for this, you can use your frozen supply in a bottle if your baby will take it and you can have a break while someone else has baby. I don't go longer than 4 hours away from mine at the moment as my breasts get sore. But 4 hours with my partner or my mum is a nice break for me.
If in the fridge, do you add to it through the day or would this not be safe due to time lapsing?
I refrigerate occasionally the day before if I know that my partner is taking him out for a few hours the next day so pointless freezing it. I don't add to it in this case as I'm sure I read that you shouldn't mix breast milk of different temperatures. So I'll put each amount in the fridge separately and combine them when they're all cold. The milk keeps a few days in the fridge but I only ever do it if it's going to be used the next day. Otherwise I freeze.
Do you feed then immediately sterilise? Or can you keep adding during the day and sterilise at the end of the day?/ after a few feeds?
Not sure what you mean. The haakaa is just used to collect the milk, not for feeding. I freeze it and when needed it's put into a bottle. I only use one haakaa at a time before washing and putting in the steriliser which I switch on at the end of the day. Although now I only use the haakaas at night so switch on the next day. My let down will fill at least 50-60 ml, if not the whole haakaa so I just freeze that immediately. If you're not getting that much out then I'd probably pop it in the fridge, use another haakaa again later and do the same. Then later on when you've a few cold in the fridge you can combine them and use them within a few days or freeze.
Can you actually wear them out and about or are they really obvious?!
They'd fall off! No reason you couldn't use one when sitting down to feed I suppose. I wouldn't though as what would you do with it? If I have some fast let down out and about I prefer to just quickly hand express a bit into a muslin to ease the flow.
I cannot tell you how many times I've fed baby in the night with a haakaa on opposite breast. Then 20 minutes later I'm practically falling asleep while he feeds and the fucking thing pops off me because it's full and soaks the bed with breast milk. I'm more careful now so hasn't happened in a while. But the seething rage of suddenly being drenched and then having to sleep on a towel after an already disturbed night with a baby is indescribable
How much milk did you collect per feed? Did you feel they were worthwhile?
So worthwhile! Maybe start with one haakaa. I did and then within a couple of days ordered two more. I could probably have used more in the early days because of the fast let down. I was filling them like mad. But the supply has settled now and 3 is enough to get by with. Love them so much!
Sounds like you found them really useful - I’ll give them a go! X