My overall feeling about this product is pretty good. I have used these models (I got a pair) for nearly half a month, and things were fine, no problem occurred. I think it's worthwhile to buy the 40G transceivers online if the good service before & after purchase could be ensured.
Pre-purchase consultation
I wasn’t quite sure whether the modules I wanted to buy could be used on my Cisco switch. Therefore, I asked the fs technicians and they told me it could. They were very patient and professional. No matter how simple the question I asked, they replied with details.
Logistics
To be honest, when I placed the order, I was worried that the logistics would not be strong because of my urgent need. It turned out I thought too much about it. The logistics were very fast, received in about three days.
Package
The packaging was good with no damage, which should be praised. And there was no difference with the picture shown on the website.
Using experience
Last but most important, they worked well with my switch. The signal transmission was stable and there was no signal loss or module failure. Everything’s fine just like the original Cisco modules I used before. Maybe I will get another two for network expansion.

One of my customers said that their Network Equipment needs to be equipped with 40G SR transceivers via LC cables. I knew Cisco 40G SR BiDi was what I needed, and I found the Cisco compatible 40G QSFP BiDi optics on FS website, added them to the cart and planned to get some matched fiber cables together with the modules. I inquired the sales rep online. The rep replied to me in several seconds and kindly reminded me that the 40G SR BiDi transceiver ran a single LC link for Rx & Tx separately, each link 20Gbps, two LC links in total gives 40Gbps connection, so it should work with LC duplex cables, and the guy sent the product links of LC cables to me. Hmmm, a very clear and timely answer, good. I purchased the modules and cables together, no bad remarks come from my customers so far.

Recommended by a friend. He told me that the products performed well and the price was relatively favorable. So, I decided to take a chance here. Unexpectedly, their service and products are awesome.
We needed 40G optical modules (better not MPO/MTP interface) for our Cisco switch. The transmission distance was about 100 meters. After receiving our requirements, fs technician recommended this transceiver to us. It could be compatible with our device and it was designed with LC duplex interface. We ordered a pair of this type (Cisco compatible) and received them quickly. We checked them carefully, no scratches or traces of use. And they work perfectly with our switch. Now, we are considering buying some 100G modules...

Give them 5 stars for fast delivery and great performance. I needed to set up a 40G network. After asking for opinions, I was told that optical transceivers and cable from fs.com worked well. So at first I bought two to do tests based on the recommendation and their performances are excellent. Then I bought these customized modules and LC cables from fs.com. Several days later, I received my packets. All of them were well packed with nothing broken. I install four modules for Fortinet FortiSwitch 1048E. Setting up on my Fortigate switches was super easy. Now they work perfectly with switches, enough for the link lengths of 100m. All of them work without a hitch. In one word, they are really good stuff saving a great amount of money without performance sacrifice. I’ll buy more of these when I need transceivers next time.

The transceivers were delivered to me very quickly after my purchase. I used it on my Cisco switch. One and a half month has passed, they still worked very smoothly, without any malfunction. What impressed me most was that my sales rep always gave me an immediate reply when I had questions about the products. Also, she contacted me regularly to care about my conditions of using.

There was a problem occurred in our project recently. The 40G optics we used to connect the Cisco N9K switch and Intell adapters didn’t work, so we had to buy other replacements. I inquired fs online and asked if they had some solutions to fix this. FS offered two solutions for us, one was to use 40G BiDi optics with LC fiber cables, the other was to use 40G SR modules with female MTP cables. Since we already had QSFP BD modules and some LC fiber cables, considering the cost and time, we chose the solution one because the service rep told me they had QSFP BD optics in stock, and I ordered four pcs. Well, the most important point I want to explain was their considerate shipping services. FS knew the time was what I cared about most, so they packaged immediately on the day when I placed the order and delivered it to me in three business days! Many thanks to them, I'm pretty pleased with this purchase.

Last month, I customized an array of QSFP-BD-40G transceivers for our network build project between two sites. I received them in perfect condition after my order. But when we used the transceivers on a switch, something went wrong. FS technicians helped us find the reason: the port configuration of our switch was not correct.Now, they work fine with our equipment.

Very easy to install. We have used these on our cisco switches and all of them work great. I haven’t noticed any issues so far. The customer service also emailed to make sure I placed the right order. These were all worth 5 stars.

Watched a video (pretty good) introducing fs transceivers by coincidence and finally decided to make a purchase here. Didn’t disappoint me. Firstly, nice package with fast delivery. Secondly, supports transmission distance I need (about 120 meters), which is important for me. Thirdly, works well.

Got a pair of this transceiver for my Cisco switch. The delivery is relatively faster compared with other vendors. And the two transceivers work well with my switch. That’s what I value most.