So I got one of these, the F1s developers kit, the more expensive one. I ordered in December last year and after a multitude of delays, one of which gave me a quite expensive free toy(!!!) this July, I finally got the F1s near the end of October. Here is my take on it:
First and foremost, the reason I got it is because the toy has 10 sensors (if I remember correctly) that record all kinds of information about what's going on inside the toy and mainly the sensations the silicone sleeve your cock goes in is experiencing. It's like the sleeve is "alive" and knows what's going on with your cock. It records the internal pressure on the sleeve, temperature in different parts inside the toy and it even records your strokes or when you move the toy up and down on your erection. Pretty cool stuff. When connected to the app on your phone, you can see what's going on with these readings.
Unfortunately, the computer program that's supposed to accompany the F1s and work with the app is not available yet. It will be in the future, according to customer service, but no idea when. Without that program, you can't use the data for anything. What Lelo intends is for the user to be able to work with the data the toy collects to dial in the exact pattern of combined vibration and sonic pulsation that the toy shells out to tailor make your own personal F1s "pattern" for optimal pleasure. THAT'S why I got the toy in the first place!!! Hopefully they release the program soon...
On to use and for us large dicked men, the pros and cons:
I'm like 7.75" on average bone pressed but when I'm so hard I can feel it in my tailbone I'm very close to 8". I wrote customer service when I was considering buying it last year and told them my measurements and if I'm too big for the toy. They assured me I wasn't, I just wasn't going to experience exactly what the toy offers because my whole cock won't be inside the toy. I went for it anyway. I'm 5.25-5.4"inches girth also depending on how hard I am, which is about the maximum girth you can be and still get inside the toy. When fully hard I have to push really fucking hard to get my head all the way to the end of the sleeve. I worry that if I force it too much, something inside the chamber might break.
Once in it feels quite exquisite!! It's very very hard to explain or describe what the toy does. The vibe for the sleeve is near the base at the orifice. It's to one side of the sleeve but it rattles the whole sleeve since it's like inside the base of the sleeve. If you are between 5-6"inches long, it will be at the base of your cock and it will feel completely unbelievable I'm sure!!! But for me it's almost midway up my shaft, so it's a bit "off" feeling. Still great when I pull the toy off me and focus attention on the last third of my cock and the head. The vibration, at least as I experience it, is extreme. It's almost too much at halfway, but that's just me.
Near the top of the sleeve is where, I think, the sonic pulse comes from. It's like a cone and there's a slight divot where your frenulum meets the sleeve. When that thing is turned up past 50% I can feel it deep inside my cock and it sends the pulse down my shaft. To feel the sonic waves pass through your glans is amazing; it gives such a unique pleasure to my glans it can be too intense sometimes. But it gets me off in ways I've never been able to get off before.
I went a little buck wild with it on my third use and fucked it kind of hard (I had it in a dock I made for Fleshlights). I must have fucked it too hard because it turned off on its own! I had to make the app turn it back on and then I took it a little easier and it stayed on. I let the toy finish me while I was inside it and its the only thing that feels as close to being finished inside a mouth as I've ever felt from a toy before. I also used it during an Aneros prostate session and while I wasn't completely hard, it made me have about a dozen orgasms. So that was cool!
I actually like not being fully hard when I use it so I can get completely inside the toy. It might not "finish me off" like this, but the sensations are wonderful and unique; worth feeling even without a boner. It's also fun to feel the toy make me get hard and then go a little flaccid over and over because the toy gauges the change in pressure from the change in my erection and alters the vibrations and sonic pulse strength. So it's great for edging while not fully hard, or something like that!
Biggest drawback is that it's noisy! It rattles a good bit pretty loudly, like a loud buzzing inside the chamber. May be a defect, not sure. I need to ask customer service. Lower settings it just hums, but as it gets to 50% it rattles. Could be my size forcing contact with components inside the chamber.
Overall it's a very fun toy but can't be it's best until Lelo releases that program that works with the app data. I certainly have never felt anything like it before (at least no human has given me, myself included, the kind of stimulation this toy can give). And it's a unique way to cum.
Hope some of this info is useful! Especially to prospective buyers