You're correct. The direct access can access the becm, but not on the vehicle.
We have to strip the becm down & access the chips directly, Hence, this cannot be performed on the vehicle, or at the roadside for that matter, although some people try, including me in the past, but the risks involved just aren't worth the risk of the becm failing completely.
I've had this argument many times in the past, where people have managed to aquire the direct access software which allows them to access an alarmed becm & then they advertise as becm's unlockers & some even go as far as saying they can repair, when in fact, they can't no matter what they tell you, & a few chaps on this forum has experianced exactly this.
There's a few chaps who advertise on line as becm specialist's when in fact, these chaps used to come to my workshop, watch & ask a few questions, then before i know it, they're advertising themselves. I find it hilarious, until they come unstuck & receive demands for refunds, then they disappear.
As for parts, we've spent thousands over the years aquiring components. We have them all & now you can't buy these anymore. Our solder stations cost more than their vehicles. Our guarentees allow a scope that if we F**k up, we will supply a fully rebuit becm FOC, & that doesn't stop at the Becm's, we repair engine management ECU's also.
I've got no problem in protecting our business, no one can meet our standards & experiance, & there's not one other than can say they are indeed, Main Dealer recommended.
We give advice to anyone that asks, & if I haven't had to time to peruse the forums anyone is more than welcome to PM me if they need advice or help