Hi Carys, i have used lc hpts for a while and have only had bfn's. Although i do throw them away after about 10mins i have been known to pull then out of the bin hours later to obsess over the result (lol) just to see if i have missed anything Crazy i know but ttc does that to you.
Positive news for you is that i have never ever had an evap line from them!!! but i dont use the midstream, i use the cup/dip ones.
I would assume they are similar because they are from the same company. I hope yours is really a bfp. Will you test again tomorrow?