We have long hoped that NEC would come up with sexier monikers than "MR04LN", but it seems they don't have that kind of marketing creativity, so we'll just be calling this model the "04", and the previous model the "03" when spelling out the entire model name gets tiresome.

The first thing to note is that while the MR03LN brought Bluetooth and wireless AC, the MR04LN is merely an evolution as far as those two points are concerned.

For the most part, the 04 does the same things the 03 does, but it does them better.

For example, with the 03, we had a hard time setting it up out of the box in order to add the APN we needed to use the eMobile SIM we tested it with.  We couldn't get the login page to work on the computer, etc.

With the 04, you can actually set up the APN from the screen directly, no computer needed!

The first major new feature is support for LTE Advanced/Carrier Aggregation this theoretically means faster speeds on supported networks.  

The other major feature than the 04LN has is dual-SIM card support.  

There are a number of possible use cases for this, but one would be for people who travel internationally a lot and would like to carry a single router keep both a Japanese SIM and foreign SIM inserted.

Another use some people have suggested it to keep two SIM cards, one with unlimited but slower speed, and one with higher speed but a monthly limit.  An alternative I can think of would be to have SIM cards from two different carriers in case you want to increase your chance of having good coverage.  

In fact, one of the merits is that it supports all of the frequencies used by both Au and Docomo, which means that you can use MVNO SIMs from either carrier (or both!) in this unit.  (The MR03LN was officially marketed towards Docomo SIM cards, though eMobile and presumably SoftBank, worked as well).  The main reason that NEC doesn't target eMobile and Softbank is because they don't do MVNO, and thus basically a router is always included with every contract, leaving not many people to buy stand-alone routers.  Also note that newer eMobile SIM cards use an APN that can only be used in routers with the IMEI white-listed by eMobile, meaning 3rd party routers won't work.

While these models can technically be used for international use, we had problems in field tests with the 03LN because it only supports LTE SIM cards, and many countries still only have 3G.  The 04LN works with LTE and 3G overseas.  

NEC also markets them only domestically, and as such, all documentation and the screen itself is available only in Japanese.

The only SIM card size supported is "micro", not mini or nano.  If this seems a bit odd for a brand new product being released at a time when most new phones are using Nano SIM cards, it seems stranger still that the manual warns against using nano-sim converters.  Although the reason for this restriction is unclear, we suspect many people will use converters anyway, if they already have a nano-sim they want to use.

Like the MR03LN, the 04 has an optional cradle.  The cradle is used not only for charging, but an Ethernet cable can also be plugged into the cradle, so that the 04 can act as a wireless router (or wireless bridge, depending on the setting you use) when it is in the cradle.  This means you can plug the unit into the cradle and use your home internet's data connection, so that your mobile data isn't depleted - without changing anything on your client devices.  

Apparently the cradle can also share the LTE network via Ethernet (in router mode), though we have yet to test this mode.

Other Improvements:

The 04 has the same size battery (2300mAh) as the 03, however the run time seems a bit longer.

The 04 also has improved 5GHz WiFi operation.  There are now two modes: Indoor and Outdoor.  The 5GHz WiFi ac is rated at 867 Mbps, which is crazy fast for a portable router.  In fact, you might bring this unit (with cradle) with you to use as a router for hotels which have only wired internet, as it is a lot faster than many of those dedicated mini routers.  

In the box (Cradle set version):

1. Unit itself

2. Battery

3. Micro USB Cable

4. Charger

5. Cradle

6. Ethernet cable

7. documentation