Yep. This is a basic as it gets for gadgets, just wanted to put it out there for new players.
****UPDATE**** 13th feb:
The STR build is crazy strong in PvP, simply because it picks up 2 overpowered ultimates.
Ways to counter:
Thorns of revenge [
30 second uptime, 180 second downtime] used at most twice in lamento battles (3 fights to win the match) - you cannot kill anyone with this ability up, unless you currently have about 10x their current health, and there were still times when both players died, simply because a 16k overkill crit hits the attacker back for around 50k (330% damage reflection)
So.. You have to be good at kiting away the teslas / healing the small damage from teslas. Bloodletters can lifeleech off of bleeds, and should not be attacking a gadget with thorns up. Pyromancers can use space divide to kite away / kill minions with ranged abilities, or their shield and phoenix combo to survive the 30 seconds of inability to attack the thorned gadget.
Other gadgets should begin to focusing your minions instead of you, or simply doing their best to run away from teslas - they are slow. If you're dueling a gadget, always pay attention for a blue glowing aura:

That's the thorns.
Of course, if they see that the opponent is overly aggresive they can bait them into damaging them and using thorns at the correct time.
OP lazer cannons:
These things outdamage any heals, unless you're a 60k health BL with great guardian, and even then the health goes down slowly, but steadily. They have a
20 sec uptime / 120 second downtime, so can be used twice or more in lamento fights, and long duels.. well I've used it 3 times in total once.
The way to deal with these things is running - BL's can have adrenaline rush and the phase ability to kite away / great guardian, if you think you can survive the damage. Pyros can phoenix, blink and shield away, again, stay as far away as possible, and run + keep your teleport on cooldown nonstop. You have to be aware of the position of both the gadget and his minions at all times, keeping max distance in lamento.
Blood sleet or any aoe abilities can also bring them down fairly fast, but only with luck. A bloodletter has once killed the cannons with 1 blood sleet, because they were directly on top of him, and he got a few crits off. From this I gather they have around 7k-10k hitpoints, buffed with armor and even more life from minion stats. When I re-positioned the cannons further from him, it took about 3 blood sleets to kill, but he took way too much damage. Therefore, long range AoE spam is the way to go, probably the best counter to the build.
Gadgeteers can only counter this ability with thorns themselves - the minions suicide on the player in less than a second, and the dmg reduction allows the player to survive their damage, making thorns a no question in lamento.
Also, some minions, when attacking a thorned gadget, will instead deal damage to their master, and not suicide, the tesla widgets being one of them.The same way that this build works around kiting characters it cannot beat face to face, the ultimates of this build must also be kited away - meaning it's a complete counter to melee characters.
What would happen in a perfect situation for melee against this build, is a silenced, slowed gadget gets nuked down. It's all about picking those abilities up in your skill tree, and then landing them, meaning this build is weaker 2v2 than 1v1 as there are more choices to control the fight.
Medical widgets actually heal for twice what they say, maybe it occurs twice a second, but the tooltip is bugged. We tested it and I went from 6k hp to 30k from 1 widget only - seems like roughly 80% over 13 seconds. Therefore, you have to be aggresive vs this build as much as you can, force the use of thorns and back off, force the use of teslas, and do your best to aoe them down before dying / run away. During this time this build will be able to heal back to full with medical widgets - rotate your CD's smartly, and keep pressure as much as you can. You might think that 1.5k damage from teslas isn't much, but when that damage is hard to avoid, and is being dealt constantly, whilst you're being kited, it adds up fairly fast.
Outlasting:
This build can also be outlasted - if you can sustain yourself and kill teslas quite fast, but are a strong enough threat to the gadget to not make him chase you and be present in the fight with melee hits, just kill the widgets. The gadget will run oom and won't be able to cast either ultimate - it all becomes a cat and mouse game.. Cinderblades do pretty well at that. Whilst their skills are fairly easy to dodge, 1 lava field will knock you to around half HP. And that's on about someone with 33k HP - 16k crits are fun to see on yourself, whislt you are also slowed and a crazy pyro whom you just kited for half an hour is finally getting some blood out of you.
(yeah.. whatever class you are and you want to PvP, stack some hitpoints. Don't let Freezin one shot you)