Disclaimer: Arcam supplied MusicBOOST for the purposes of a forthcoming Headfonia review. It goes for 100£ - 120£. You can learn about it here: MusicBoost - Arcam.
RMAA: iPhone 6
RMAA: iPhone 4s
RMAA: Chord Mojo
Review: Venturecraft GoDAP
I've used cases (or makeshift substitutes) since 2007, but never seriously considered a charging case. I don't need the bulk. And, my Quad Lock fastens to a bicycle like a camera lens to a camera. Amazing.
MusicBOOST is late to an already late party. Around the corner is the iPhone 7. If you're a big iPhone 6 fan, you're good for at least a year. But when you upgrade or move on, you'll be up against a wall. And, unlike generic amps and DACs, MusicBOOST will suffer precipitously falling secondhand sale prices.
MusicBOOST sounds like an iPhone 4s, which, at least to me, is a good thing. Well, it should be. It hisses more than a 4s, which is a bugger for owners of sensitive earphones such as Shure's SE846 and Ultrasone's IQ. Evidently, its amp is more powerful than the iPhone 6's. But in practice I get less measurable volume from it through a pair of 600Ω Beyerdynamic DT880s.
MusicBOOST charges the iPhone. It half protects it. And, it sounds like an iPhone 4s - which in my books is a good thing. The biggest audible benefit it brings to table is a stabler loaded signal, with smaller upticks of THD and IMD against base signals.
The following Rightmark Audio Analyzer tests were conducted through this equipment.
Source: Arcam MusicBOOST
ADC: Lynx Studio HILO LT-TB
Computer: 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$); bespoke y-split 2,5 TRRS to dual 3-pin XLR made by Musashi Sound Technology.
NL - no load
SM2 - Earsonics SM2
S7 - Audio Technica ES7
DT880 - Beyerdynamic DT880
24-bit TARGETS and loads (+0dB)
24-bit summary (+0dB)
Honestly, Arcam didn't bring anything important to the table. Even Apple have a charging case. Amp/DAC cases have been done before. MusicBOOST doesn't stick out enough. It melds functionality of both markets in ways too familiar or mundane. It's as solid a product as exists in its wishy-washy market.
Someone with vision, follow through, and a quality factory: put this market to rest.