Comparing the different QSFP28 variants, depending on your cabling and application. To make it easier FLEXOPTIX created an overview with all the different variants, without Active-Optical-Cables and Direct-Attached-Cables.

 housing_16_qsfp28_std_lc_1  housing_69_qsfp28_std_mpo_1

 
The main difference between Q.161HG.x and Q.85/131HG.x is the connector type. QSFP28 like Q.161HG.x do have an integrated LAN-WDM Mux/Demux which multiplexes all 4 lanes to only one fiber. The same for Q.161HG.x.C/CL but with CWDM Mux/Demux. This gives the ability to use a LC-Duplex connector with a standard Multimode- or Singlemode-Fiber.

QSFP28 with MTP/MPO connector are more price sensitive. There is just a cabling with MTP/MPO cables needed.
 

Description/
Connector
Distance Wavelength Connector Details Interoperability  Types
QSFP28
SR4
70m (OM3)
100m (OM4)
4 x 850nm MTP/MPO IEEE 802.3ba
(100GBASE-SR4)
SFP28 SR Q.851HG.02
(Ethernet)
Q.851HG.02.F
(Eth, OTU4, FC)
QSFP28
PIR4
2km
(G.652)
4 x 1310nm MTP/MPO 4 x 25/28G operations on SMF SFP28 LR Q.131HG.2
(Ethernet)
QSFP28
IR4/LR4 lite
2km
(G.652)
1295.56nm,
1300.05nm,
1304.58nm,
1309.14nm
LC 4-Channel LAN-WDM Mux/Demux inside  QSFP28 LR4 Q.161HG.2
(Ethernet)
Q.161HG.2.F
(Eth, OTU4, FC)
QSFP28
CWDM4/CLR4
2km
(G.652)
1271nm,
1291nm,
1311nm,
1331nm
LC IEEE 802.3ba
(100GBASE-CWDM4)4-Channel CWDM Mux/Demux inside
CWDM SFP28 Q.161HG.2.C
(Host with FEC required)
Q.161HG.2.CL
QSFP28 LR4 10km (G.652) 1295.56nm,
1300.05nm,
1304.58nm,
1309.14nm
LC IEEE 802.3ba
(100GBASE-LR4)4-Channel LAN Mux/Demux inside
SFP28 LR
QSFP28 IR4
Q.161HG.10
(Ethernet)
Q.161HG.10.F
(Eth, OTU4, FC)
QSFP28 CLR4+ 10km (G.652) 1271nm,
1291nm,
1311nm,
1331nm
LC 4-Channel CWDM Mux/Demux inside QSFP28 CWDM4
SFP28 CWDM
Q.161HG.10.CL
QSFP28 ER4 lite 25km (G.652) 1295.56nm,
1300.05nm,
1304.58nm,
1309.14nm
LC 4-Channel LAN Mux/Demux inside QSFP28 LR4
SFP28 LR
Q.161HG.25
(Ethernet)
Q.161HG.25.F
(Eth, OTU4, FC)
Q.161HG.25.TXO
(Tx Optimized)

 
Note: a QSFP28 LR4 is interoperable with a QSFP28 LR4. I didn't mention this in the columen "interoperability" for a better overview. This applies to all other types as well.

From a technical point of view a "split operation" is possible with all QSFP28 mentioned above. QSFP28 get always 4 x 25G/28G from the host on the electrical side. Only the programming of the transceiver needs to be adapted for the host. On the optical path you have to check how to split up the signal in 4 dedicated 25G/28G lines. For the ones with MTP/MPO receptacle this is not a problem with breakout-cables.

For connecting to SFP28 please have a look on the available SFP28 transceivers.
P.8525G.01
P.1325G.2
P.1325G.10
P.1328G.10