I use a Mini Protank 3 on standard ego sized batteries, fits perfectly and if a silver Ego it looks seamless.
I also have - and recommend - the Aerotank and I have a Protank 3 also, but the airflow is a little tight for my preferred 100% VG juices.
Kanger products while not particularly blingy or fashionable are well crafted solid little pieces with easily replaceable and easily sourceable coils which can be ordered fairly cheaply in bulk. Also, there is little chance of Kanger discontinuing their atty heads a year down the line when they release new models.
Having said that, my local vape shop has now started stocking the newer style PT3, Mini PT3 and Aerotank atty heads with the internal, clearamiser style coils and wicks, so I can no longer rebuild them. It's not difficult finding the Kanger dual coil multi atty heads with external wicks online though fortunately.
The RBA's with glass or PC or acrylic windows - such as the Squape, Kayfun, Rocket or Rose V2 are excellent investments once you're comfortable with rebuilding and you have the proper equipment, such as an Ohm meter at the very least. It also requires a fair bit of patience, manual dexterity and a basic understanding of Ohm's law, as well as good quality batteries and chargers.
Getting an Aerotank, or Mini Protank 3 if you want something slimmer is a lot less hassle, lighter on the wallet and is easily maintained. The coils are decent and the flavour is pretty good, not as good as a top end RBA or clone, but several tiers above a CE5 or similar.
The one advantage of the newer style Kanger atty heads is the resistance though. The one that came pre-installed in my Mini PT3 is 1.5 Ohm's resistance, down considerably from the 2.0 and 2.5 Ohm heads that were available when I purchased my Aerotank. I understand they even sell a 1.2 Ohm and a 0.8 Ohm head now also!
It's a good time to buy an inexpensive pyrex clearamiser ;D