(Drafted this months ago, but not sure if it'll make much sense to anyone unless you've actually used the readers, but you never know. And don't want to make this sound like Zettle (now called Paypal) is particularly problematic, since some people seem to have used it for ages without the persistent reliability problems I've had over the years...)
Anyway, have been meaning to post something here on the Zettle v Lopay, now I've got both readers
One immediate impression with Lopay was that I seemed to be getting endless promotional emails trying to get me to do stuff, which I found a bit annoying, but they seemed to dry up after a few weeks.
And can't be bothered looking back now (because I've largely forgotten about it all), but Lopay's commission rates and stuff are a lot more complex than Zettle's. I posted about the international/domestic cards and the differences in rates above, but there are also several different options for speed of payment to your bank account (including immediate, I think, but obviously the rate for that is higher).
But I quickly forgot about that, and maybe using Zettle for some cards and Lopay for another, because it's difficult to work out which cards are domestic, and which are international, or whatever. Of course, you can largely guess based on who's doing the payment (overseas tourist v local drunk, or whatever), but in the end I decided that just getting the reader up and running and getting the payment done was more important than fannying about trying to work out what kind of card it was etc.
Anyway, after a few teething problems with connecting the reader etc, the Lopay thing does seem a bit more reliable and responsive than Zettle, but it's really a mixed picture, and in some ways Zettle is a bit better. And I lost one Lopay payment the other week, and not sure if it was my fault or Lopay's, but it was deffo £5 or so that disappeared
But I've actually started using Zettle again as my main reader, and using Lopay as the backup
(Months later I'm doing it the other way round again

)
And the readers are quite different beasts in terms of charging etc. The Zettle reader can last a few days without touching it, and if all's going well I can just open the app, key in the fare, and it'll fire up in seconds.
The Lopay reader just can't be left active for days because it's either active and it'll run down the battery after a few hours, or it's totally off, and it's a wee bit of a fanny to get it connected again (although, to be fair, it doesn't take that long if all's going well).
But the Zettle reader goes pretty dormant after a few minutes of using it, so to that extent it doesn't run down the battery, and if all's going well it'll fire up immediately even after being untouched for a couple of days.
The Lopay screen still displays something even after it's not been used for half and hour, say, while the Zettle reader displays nothing after a few minutes, thus it's probably in a more dormant state, thus the battery will last longer.
And one thing that caught me out initially is that if the Lopay app is closed (on an Android phone at least) then that'll disconnect it from the reader, and the reader will soon power off completely. Which is good in that it retains the charge, but bad in that it's not so easy to reconnect when it's used again. So basically keeping the Lopay app open on the phone in the background keeps it up and running, but drains the battery. (So at the end of a shift you need to close the app properly on the phone to close the reader, or what's left of the battery charge will soon drain. Of course, if the reader and phone are sufficiently far apart in terms of bluetooth signal then it'll disconnect anyway, and thus will retain the battery charge on the reader.)
On the other hand, I'm not sure if it makes any difference whether the Zettle app is closed after use. I think the reader will soon go into a dormant state either way, thus retaining the battery. (Of course, if you've got your reader connected to a power source then all that's pretty irrelevant, but I usually charge mine at home, and not in the car unless I've forgotten to charge it, or whatever...)
There are also a couple of practical things that I don't like about the Lopay system, such as smaller numbers on the app when keying in the fare - I ideally need to put my reading glasses on to see the numbers, while the bigger digits on the Zettle app mean it's not a problem seeing them
The Lopay app just seems a whole lot cluttered as well, with adverts and the like, and the payments history (for example), just doesn't seem as clear as with the Zettle stuff.