My vote would be a separate hot air and many irons with a selection of tips already mounted. I don't want to wait for the iron to cool before i change tips. I have a 2 in 1 a KADA cheapy, had it a few years and it works well. If you look on youtube there is a Factory video of KADA, look closer and you will see that they not only make KADA but Aoyue and several other brands too. From looking at the Blackjack, that is also from the same factory! there is noting to choose from them.
pretty much we are same here, except our opinion on KADA. you see, mine is just several months, and it started playing up (the iron only, not hot air), sometime it cannot sense the temp correctly and fail to reach the set temp. workaround? bang it on the bench or punch the unit several time on it face or "masturb" the connector several time! then it fixed that. maybe it got loose connection somewhere, havent had any time to inspect carefully as it's not really serious, but sometime i got sick as well. i thought i'm gonna hack it someday! put my own PIC and program or something.
so for serious purpose, i
dont recommend KADA. but as my previous recommendation, its the same as dimlow... get separate unit. so since you have mentioned that, here is the KADA. noticed the sticker i put on? i have to put that coz the switches are on the wrong side, the iron is on my right, but its switch is on the left, so i have to put the sticker to remind me, ergonomics sux! i onced opened the unit try to "switch" the switches, but its not as easy as i thought
and note the tape around the hot air? its been broken opened, veru poor assembly and durability
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i also have a single soldering iron (hakko presto, second pic) its been years with me, and how it works? harder than rock! if i want to give rating for both, i'll give 2in1 KADA 5/10 mostly due to its iron unreliability. and the hakko is 9/10, minus one only due to it doesnt have any temperature control, but has been 150% reliable and 10th time cheaper than KADA!