Hi, complete greenhorn here. I found the technology very interesting, want to try some implant, but not sure which is the best. So there are my questions:
Also have a read through the other topics here to make an educated decision 
Check what you want to do, get inspired, then choose the right chip(s).
Cheers buddy, NExT looks to be fine for me. Is cyborg.ksecsolutions.com legit site for buying DT products?
NExT is a great choice for a starter implant!
And yep, I’ve never ordered from them since DT shipping is faster to my part of the world, but for the UK they are the go-to.
They are the official distributor over that side of the pond, and @KaiCastledine from KSEC frequents here - If you ask him nicely, he can probably PM you instructions on joining the KSEC Cyborg Memberships to get a discount code for your order too!
Great stuff! But still I will give some more time to research as I don’t want to rush with this 
Good call! Definitely pays to do your research, if you do have any questions or find anything confusing, let us know 
Good mention ! @Pet you can find details of this here: https://cyborg.ksecsolutions.com/ksec-cyborg-exclusive/
OK, spent last days doing research. I’m undecided between NExT and Vivokey Spark 2 (I know there’s bundle I can get both, but I won’t use 2 implants). Which one of those is better? For bitcoin cold wallet, some contacts and possibly for unlocking some smart devices? I don’t want any implant which will become outdated after few years of course. And main question is - is it possible to write multiple records on those implants? Or there can be just one record - task, and any other will just re-write previous?
What you want sounds like the NExT.
Yeah you can put multiple records on the NFC side, but most phones will just use the first one.
So you could have one contact, probably also a cold storage wallet if the app reads all records.
And you can unlock as many things as you like if you enroll your implant to those things.
I don’t think a next will be outdated very soon, there are just too many systems using compatible hardware.
What about xDF2 DESFire EV2 8kB NFC? Is that same kind of chip as NeXT only with more functions and extended memory as I understand?
TL;DR for you, yeah kinda, but not really
It’s complicated and I’m kinda new. But as far as I know for your main purpose (cold storage and contact) you could use it.
The DF2 is impressive as you can store a contact with picture.
But no it’s not the same, the DF chips can do some magic the xnt/next cant, e.g. random uid or internal “payments” or be a bus ticket.
Afaik transportation companies could, but dont want to, give you some keys and let you enter the bus with the implant in some cities. (Same problem with everyone else that uses DF2 cards.)
If you plan to build your own secure systems go DF2, for your stated cases a next would be enough, but I believe you can do the same with the DF2 with more storage. So from your view, it might be the same, but in reality the DF2 is a little cooler.
On the other hand the next includes another chip on another frequency which you might find handy some day (work badge or whatever.).
Don’t take this for granted, wait for others to respond. Or just search the forum, all your questions were answered before in some way.
And yeah if I’d choose… I’d pick xSIID ^^.
Tech wise there vastly different. The next is a 2 in one implant that has the capability to emulate most LF tags (t5577 chip) and a HF tag called a ntag216 that has a static uid and 888 bytes of user storage. The df2 is a type 4 NFC HF chip with more memory and advanced features than the ntag216 but it’s not simply an upgrade, there are some applications that theoretically only work with an ntag216 that a df2 would not replace and vice versa, the df2 also has no LF side, it’s purely a HF chip.