Both are 40W box mods with built-in batteries and no 18650s to buy, which makes them perfect first mods or MTL workhorses. The GTX One Pro has the bigger battery and the lower price; the iStick i40 adds variable voltage and a 1W floor. Here is the full comparison.
The short version
- iStick i40: £27.99, 2600mAh, 1 to 40W or 0.5 to 8V, 98g.
- GTX One Pro: £19.99, 3000mAh, 5 to 40W, 0.87-inch OLED, 92g.
- Both have 2A fast charging and a 510 connection.
- The GTX wins on value and battery; the i40 wins on fine control.
The spec sheet
A small mod with a built-in battery is the simplest way to step up from a pod kit. You get variable power and a 510 connection for any tank, without learning about external batteries.
The Eleaf iStick i40 packs 2600mAh, runs from 1 to 40W, and also offers a variable voltage mode from 0.5 to 8V. The Vaporesso GTX One Pro packs 3000mAh, runs from 5 to 40W, and has a 0.87-inch OLED screen and Smart mode.
Both support 2A fast charging over USB-C, and both weigh under 100g.
Neither needs a spare battery in your bag.
Battery and value
The GTX One Pro has 400mAh more battery, about 15% extra, and costs £8 less. That is an unusually clear win in a single category.
Vaporesso quote around 90 minutes for a full charge. At typical MTL settings of 10 to 15W, either mod should last a full day for most vapers, and a lot longer for light users.
Built-in batteries are convenient but they do age. After a few hundred charge cycles, capacity drops and the mod needs charging more often. That is true of every built-in battery device, including your phone, and it is the main trade-off against an 18650 mod where you can swap cells.
Source: Manufacturer specs as listed on Spectrum Vaping.
Control: watts or volts
The i40's variable voltage mode is a throwback that some experienced vapers still love. Instead of setting watts, you set volts, and the mod delivers whatever power that produces on your coil. It is how mods worked before variable wattage took over.
The i40 also goes down to 1W, which is useful for very high resistance MTL coils that want gentle heat. The GTX starts at 5W.
For most people, variable wattage is easier to understand. If you have never missed volts, you will not miss them on the GTX. If you have, the i40 is one of the few modern compact mods that still offers it.
- 1Wi40 minimum
- 5WGTX minimum
- 12W1.2 ohm MTL coil
- 25WRestricted lung coil
- 40WBoth maximum
Which tank to put on top
A 40W mod is the perfect partner for a mouth to lung tank or a restricted direct to lung tank. It is not a cloud machine, and that is a strength: it sips liquid and battery.
Good matches include the Aspire Nautilus 3 or the Innokin Prism T18E Pro for MTL. Pair either with 50/50 or nic salt liquids. Nicotine is addictive, and an MTL setup usually runs higher strengths than a sub-ohm rig, so match your current level.
Avoid low ohm sub-ohm coils that ask for 60W or more. The mod will cap out and the coil will feel weak.
What do you want from a small mod?
GTX One Pro, 3000mAh for £19.99.
iStick i40, with 0.5 to 8V.
iStick i40, which goes down to 1W.
GTX One Pro, which sets power for your coil.
Eleaf iStick i40
The iStick i40 is a minimalist box that sits easily in a pocket. It comes in Black, Cyan, Fuchsia Pink, Greenery and Neon Orange.
Its 2600mAh battery is enough for a full day of MTL vaping for most people, and 2A fast charging over USB-C keeps downtime short. Eleaf pitch it as a companion to a wide variety of tanks, supporting MTL, RDTL and DTL depending on what you fit.
If you want a mod with personality and old-school voltage control, this is it.
Pair it with a Nautilus 3 and you have a compact setup that will run for years with only coil changes.
Vaporesso GTX One Pro
The GTX One Pro is slim, simple and very good value. It comes in Black, Silver, Blue, Red, Pink and Brown, and weighs 92g.
Smart mode reads your coil and picks a sensible wattage, which makes it a friendly first mod. The 0.87-inch OLED screen shows your settings at a glance.
For £19.99 with a 3000mAh battery, it is hard to beat as a compact daily mod. Have a look at what is in stock below.
Pop an MTL tank on top, fill it with 50/50, and you have a setup that sips battery and liquid all day long without asking anything of you.
Quick answers
Do the iStick i40 and GTX One Pro need batteries?
No. Both have built-in batteries: 2600mAh in the i40 and 3000mAh in the GTX One Pro.
Which is better for mouth to lung vaping?
Both are excellent MTL mods. The i40 goes down to 1W for high resistance coils; the GTX is cheaper with a bigger battery.
Can these mods run sub-ohm tanks?
Only gentle restricted lung coils. At 40W maximum, they are not designed for low ohm coils that need 60W or more.
What is variable voltage?
Setting volts instead of watts. The iStick i40 offers 0.5 to 8V; the mod then delivers whatever power that produces on your coil.
