How long do these last?

I have had mine for 6 months and they are still in perfect condition. I don't know how long they will last but am so pleased with them I have bought more for my children to use.

We have a washer-dryer. Does anyone know if we can chuck them in at the beginning of the wash/dry programme?

You can but I would not. It would defeat the whole objective of the balls. They are there to SAVE power and increase the effectiveness by fluffing the fibres of the washing making your clothes feel better. If you 'chucked them in at the beginnin' you would be wasting power and water by effectively washing the balls and taking more power to dry the balls out. The balls will hold a lot of water and it will go deep. This means you would not be drying the balls out. Your washing would not be dry and it would take a lot more time and effort to dry the balls out for use. In addition your cleaning detergent would not go as far the balls would absorb a heck of a lot of the powder. The rinse function which effectively cleans your clothes. (The powder looses the dirt the rinsing action cleans the dirt from them.In essence it's a bit like hanging your washing out to dry in the rain.

How do you know when theyve stopped working effectively?

Wooly Tumblers are guaranteed to last for 1,000 loads because of their natural durability. So if for example you use them in your dryer twice a week, they will last 9 years and a half! Care & Instructions Caring for your Wooly Tumblers is simple, because they are 100% natural they last for 1,000 washes. Always make sure you put your dryer balls in with other laundry, so the dryer does not batter them too vigorously. If they ever need washing or you fancy freshening them up, put the balls in a pillowcase or lingerie bag into the washer with a few bed sheets or similar items, and run the washer as usual on a low heat cycle. To dry them, leave out in direct sunlight for a few hours. The sun will naturally whiten them. Or you can dry them with another load of washing in the dryer! Why not store your Wooly Tumblers in the dryer, so they are always there to soften and plump your clothes naturally.

I have a washer dryer and after the drying program, washing doesn’t smell fresh. Can I add drops of essential oils to wool balls to improve this?

Yes and I have but in dryer only as the wash will wash the oils out. I had previous balls which once wet, even tho washed, I had to bin as they made washing smell every time and eventually disintergrated. If using a washer dryer suggest new balls and add before the dryer function starts (ie don’t use with continuous run cycle)