did you actually buy the Barlow lens at that link?
Yes, although the seller was operating under a different name ("fyscope" IIRC, though they also sold socks?!) at the time. I'm quite impressed by the quality of mine, though would expect that if you buy a few of them, they will probably vary somewhat. The fyscope microscopes and accessories look absolutely identical to the amscope offerings. Not sure if they are reworked seconds or what, but I can say that my scope works great (except that the LED light build quality) including the 0.5x Barlow.
I've never purchased via Aliexpress - are there any issues or gotchas to be aware of? The price certainly looks good.
Mainly that it's addictive. For me in NZ, it's more-or-less the only sane way to get a lot of my tools and parts. There are definitely knock off items on there, with varying quality, so if it's advertised as being a well-known brand with a super low cost, then don't expect it to actually be the real item (eg Bonpens).
The "free shipping" option is quite variable in time - it generally takes things between 2 and 4 weeks to arrive here from China. The DHL/UPS/FedEx options are very fast. The missing cost in shipping from China is getting covered by the domestic shipping carrier, so I imagine that situation will change.
I've only had one situation where I wanted to return something; bought a commercial-type blender which arrived with an open circuit in one of the rotor coils. The seller was quite responsive and open to options. I initially thought that it had a bad brush (one had disintegrated, in hindsight probably due to overheating), and they sent me a new set of brushes at no charge. We settled on them sending me a new "motor", which turned out to be an entire new base, for the cost of shipping.
Hope this helps! -Ian-