I'm sorry this paragraph isn't meant for you OP, I know your in England and you can't order the BB or the SB. But I hope this will help others reading this and trying to compare the SB BB and Bolt:
Pretty sure the new bolts are of higher quality than the old ones. The new ones are Anodized and they no longer have a soft rubber horn switch button. I got mine from madvapes in the Anodized Slate color. Its a hard flat button similar to the AltSmoke's BB I'm guessing. It has the same look as the BB in the video above. I've dropped it and it kept it in my pocket with change and metal drip tips and it hasn't scratched. I try to remember NOT to do those things though haha. Anodized Aluminum is as strong as the surface of steel so its very scratch resistant. If it does get scratched it usually won't scratch all the way through and instead will look like a blemish. I believe the earliest bolts had exposed wires in the switch cap as well? The new bolts do not have exposed wires and the contact pin is enclosed in a disc similar to most devices I've seen and had. I believe the pin is made of brass for good conductivity. I have read that the wires within the new Bolts are upgraded but I've heard others say they are still probably of less quality than that of the SB or the little BB. The bolt is a great 1st mod though and I don't think there are many mods that look better. The SB is fatter and chunkier and taller than the Bolt in 18650 mode. The BB is the same width as the Bolt, but I think its a little smaller? Idk.
I hope that DOES help show you that the bolt IS NOT a BAD choice for a fixed voltage tube mod. EVERY SINGLE Silver Bullet I've ever seeeen has had chips or blemishes or scratches in it's paint. I'm sure Altsmoke would have no problem repainting your SB or BB for a fee. But I've personally harped on my Bolt for a while now and haven't managed to scratch it lol. Anodized Aluminum is very strong. I hope you can find the anodized versions because they are the most up to date out of all the Bolts on different sites today. Mine hits like a champ. I mean its a truly strong 3.7v haha. It all depends on which battery I use in it. Trustfire batteries don't hold their 3.7 voltage for long, but an IMR battery hits strong all the way until it just stops working out of nowhere haha.
NO battery, not even an 18650 battery is going to last a regular vaporer 2-3 days. My 18650 bats last around a day and 1 quarter IF I choose to let them go that long. With my AW 18650 I do typically let it go for a day or almost a day, but I only use my Trustfire for an hour or two before I pop it back on the charger to get it back up to the full capacity it can throw out.
A variable voltage device is great in that you can keep it at 3.7v for the duration of your vape, its regulated. they are also great in that you can use whatever you want for carto ohm. sweeeet.

Idk I use my Smoktech telescoping mod a lot (its my newest mod) with 1.5ohm cartomizers (I actually like them a little higher, 1.8 or 2ohm or whatever is good for 3.7volts. 1.5 ohms tend to die easier. idk. But yeah, whatever man) Just go with your gut and buy the mod that weighs your wants and needs. Everybody should have at least 1 ego battery. They are $20 if you buy a single battery with a cone to screw in around your cartomizer to complete the look. I have a 900mAh eGo. Then idk, everyone should have a fixed volt big battery mod so that they can enjoy low res cartos and attys. See, u cant use anything below like 2.5 or 3ohms on an eGo without running the risk of harming your batteries or having them die prematurely. (because the battery is too small to handle that kind of thing) SO a fixed volt mod is great for low res cartos. Thats why I have a Bolt w/ 18650 sleeve. Then I always wanted a telescoping mod so that I could use whatever battery I had charged in it so I got the smoktech TSM or telescoping mod. Loving it with a standard 306 atty. I can throw a kick in it with whatever battery I want too which is DOPE. Then Idk I like to have a VV device.
IDK which one you want FIRST, or if its gonna be your ONLY one, but weigh the wants and needs (FOR NOW) and get one!!