well mifi like E5331 is built mainly for user who is always on the move with convenience wireless connection,..

while E3276 + TpLink is built best for homes usages,..

if u comparing usages at home only,. it still depending on what frequency in 3G you are connected to,
3G in malaysia = 2100Mhz & 900Mhz  ( some area only have either one ),..

so if your device conencted to 2100Mhz in 3G in your area, then it will be confirm weaker signal  than 900Mhz

the higher frequency = the lower penetration

and compare between both device E5331 & E3276,..

E5331 = mifi, built with older generation chipset from Qualcomm MDM8200A, support 3G up to HSPA+ 21Mbps

E3276 = Data card/Usb Modem built with latest huawei own  hilink chipset, support 3G up to DC-HSPA+ 42Mbps, 4G up to 150Mbps,..

also it depends on your personal budget as well,..

and one more thing, TPLink TL-MR3420 V2 original router stock firmware current DONT SUPPORT E3276 modem, u need to convert your router by flashing it to Rooter openwrt firmware,..

last thing is depends on your way of usages,.. 

plenty of factor to consider about,.. just make sure u pick the right choices,.

well mifi like E5331 is built mainly for user who is always on the move with convenience wireless connection,..

while E3276 + TpLink is built best for homes usages,..

if u comparing usages at home only,. it still depending on what frequency in 3G you are connected to,
3G in malaysia = 2100Mhz & 900Mhz  ( some area only have either one ),..

so if your device conencted to 2100Mhz in 3G in your area, then it will be confirm weaker signal  than 900Mhz

the higher frequency = the lower penetration

and compare between both device E5331 & E3276,..

E5331 = mifi, built with older generation chipset from Qualcomm MDM8200A, support 3G up to HSPA+ 21Mbps

E3276 = Data card/Usb Modem built with latest huawei own  hilink chipset, support 3G up to DC-HSPA+ 42Mbps, 4G up to 150Mbps,..

also it depends on your personal budget as well,..

and one more thing, TPLink TL-MR3420 V2 original router stock firmware current DONT SUPPORT E3276 modem, u need to convert your router by flashing it to Rooter openwrt firmware,..

last thing is depends on your way of usages,.. 

plenty of factor to consider about,.. just make sure u pick the right choices,.

check the signal in 900 or 2100MHz wise,

you can refer here -> https://forum.lowyat.net/topic/2584921

on MDMA ,. mifi currently dont support for checking frequency

mifi dont support band config in frequency as far as i know,

and blacktubi is selling E3276,.

for MR3420 V2 wise, u can get in at shop or in garages sales section under networking related item , price RM80~RM90,..

Red should work better, any instruction you need is on first page

dont try the latest version, it wont work well with your E3276,. a few bug as well,

am using huntsman 2013-11-10 red,. the best version to fit my E3276 for sure,.

Can you see this in your router?

how to flash rooter : i personally use huntsman 2013-11-10red for my TL-MR3420 V2 + E3276

your screenshot showing that u are at the correct tab backup/firmware is the section where you can flash your router firmware

the instructions/descriptions in the GUI is pretty much straightforward and obvious. You won't be getting much response if you keep asking us to spoon feed you.